Joining method for joining electrically ceramic bodies and a joining apparatus and joining agent for use in the joining method

ABSTRACT

PCT No. PCT/JP91/00560 Sec. 371 Date Feb. 28, 1992 Sec. 102(e) Date Feb. 28, 1992 PCT Filed Apr. 25, 1991 PCT Pub. No. WO92/00257 PCT Pub. Date Jan. 9, 1992.The present invention relates to a joining method, a joining apparatus and a joining agent capable of joining two bodies to be jointed in a large size or in a complicated shape in a good joining condition. Specially, the present invention is to provide an improvement in a control of the current supplying method applicable for the electrically heating of the ceramic bodies or a joining agent in an electric conduction (a elecrode switching type due to a plurality of fixed electrodes and a switching control type between two kinds of the electric power sources), a control method of a auxiliary heating, a control of the holding apparatus (the control by the free thermal expansion at the pre-heating, a adaption of a balance mechanism and a measurement of the displacement), the adjustment of the shape at the butted portion (improvement of the pipe joint structure) and a joining agent superior in the joining strength.

SPECIFICATION

The present concerns a joining method for joining electrically ceramicbodies and a joining apparatus and joining agent for use in the joiningmethod.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improvement of a joining method forjoining two ceramic bodies in a large size or in a complicated shape byheating electrically a butted portion to be jointed with, as main heatsource, Joule heat caused by supplying electric current to the portionto be jointed, and more particularly to an improved joining methodapplicable for a method described below (a joining method to supplyelectric current to a ceramic body or a joining agent having an electricconductivity at a high temperature to complete the joining process).

2. Discussion of the Prior Art

A conventional joining method for joining electrically ceramic bodies isdivided into the following four groups:

(A) A method which joins ceramic bodies by supplying electric current tothe ceramic bodies or a joining agent having an electric conductivity ata high temperature. In this case, a joining agent is inserted at buttedplanes to be jointed between the ceramic bodies to form a butted portionand the portion is preheated with an auxiliary heating method by using agas burner or a preheating means. After the ceramic bodies or thejoining agent is in an electric conduction, the electric voltage isapplied across at least two electrodes attached to the butted portion tobe jointed to flow electric current through the electric conductiveceramic body or the joining agent at a high temperature. As a result,the plane to be jointed is heated with the Joule heat caused by theelectric current flowing through the conductive ceramic body or thejoining agent, and a reaction between the joining agent and the ceramicbody is carried out to complete the joining.

(B) A method for joining ceramic bodies at least one of which has anelectric conductivity at room temperature by permitting an electriccurrent to flow through the electric conductive ceramic body in parallelto portion to be jointed.

A joining agent is inserted between the ceramic bodies at least one ofwhich has an electric conductivity at room temperature. The ceramic bodyhaving an electric conductivity has two electrodes or an electrode in abelt form linked thereto at the vicinity of the butted portion and issupplied the electric current to the conductive ceramic body for heatingthe vicinity of the butted portion by Joule heat. As a result, thejoining agent reacts with the ceramic bodies to join the butted planesof the ceramic bodies.

(C) A joining method in which an inserting member for heating having anelectric conduction at room temperature is inserted between planes to bejointed of two ceramic bodies and is heated by an electric currentflowing in parallel to the butted planes to be jointed.

(a) The inserting member for heating is composed of an electricallyconductive ceramic body having the joining agents attached to the bothsurfaces thereof and is inserted into the butted planes to be jointedbetween ceramic bodies of an insulating property or of a high electricalresistance. The both terminal surfaces of the inserting member forheating are linked with at least two electrodes or an electrode in abelt form and are heated by an electric current flowing in parallel tothe butted planes to be jointed. The Joule heat generated by theelectric current heats the butted portion and executes the reactionbetween the joining agent and the ceramic bodies to complete thejoining.

(b) The inserting member for heating is composed of an electricconductive ceramic base laminated by an insulating ceramic layer and isinserted into the butted planes to be jointed of ceramic bodies, atleast one of which is in an electric conduction or between a metal bodyand a ceramic body in such an arrangement of facing the insulatingceramic layer to the electric conductive body to be jointed. Theelectric conductive ceramic of the inserting member for heating has atleast two electrodes or a belt form electrode linked to the bothterminals thereof and is heated by an electric current flowing inparallel to the butted planes to be jointed. The Joule heat generated bythe electric current heats the butted portion and executes the reactionbetween the joining agent and planes of the ceramic bodies to completethe joining thereof.

(D) A method which joins bodies to be jointed having an electricconductivity at room temperature by permitting an electric current toflow in a direction crossing the butted planes to be jointed.

(a) A joining agent is inserted into butted planes to be jointed betweenceramic bodies having an electric conductivity or between an electricconductive ceramic body and a metal body. The ceramic bodies having anelectric conductivity or the electric conductive ceramic body and themetal body are provided with two electrodes, respectively and are heatedan electric current flowing in a direction to cross the butted planes tobe jointed. The Joule heat generated by the electric current heats thebutted portion and executes the reaction between the joining agent andthe planes of bodies to be jointed to complete the joining thereof.

(b) Butted portion to be jointed between electric conductive ceramicbodies or an electric conductive ceramic body and a metal body is formedby setting an inserting member for heating, has an electric conductivityless than that of the electric conductive ceramic body, there betweenwith a joining agent. The two bodies to be jointed are connected withtwo electrodes, respectively and are heated by an electric currentflowing in a direction to cross from one to another butted planes to bejointed. The Joule heat generated by the electric current heats thebutted portion and executes the reaction between the joining agent andthe bodies to be jointed to complete the joining thereof.

SUMMARY OF THE INVENTION

A butted portion to be jointed can be heated uniformly by fixingelectrodes or by using electrodes in a decreased number when the bodiesto be jointed are in a small size or in a simple shape. In connectionwith a joining method for joining materials in a large size having alarge joining length (or a long joint portion) or in a complicated shapeof the joint portion, the following joining methods are proposed: (1) Amethod for joining by making a relative movement between electrodes andjoining materials with a suitable moving means. (2) A method for joiningby linking a plurality of electrodes or an electrode in a belt form toan electric conducive material along with butted portion to be jointedand by applying voltage to all of the plurality of electrodes at thesame time to heat the butted portion (Japanese Patent Publication(unexamined) 1989-176282) In connection with a method (1), in order toheat uniformly the butted portion to be jointed, the method requiresmoving means for moving the electrodes or ceramic bodies in a high speedand results in a high cost and a necessity for a large space forinstalling the equipment. In addition, the movable portion for joiningrequire a many times of maintenance and a special care of the safety. Inaddition, in order to heat the butted portion to be jointed up to anecessary temperature in case of a low electric resistance of thematerials to be jointed, this method requires that an electric currentin a large range flows from the electrodes to the ceramic bodies andaccordingly requires the contact resistance as low as possible. On theother hand, the contact between the electrodes and the ceramic bodiesbecomes poor with the movement of the electrodes or the ceramic bodies.This causes an arc to generate easily at the electrode contact area andthus the ceramic bodies to be damaged or degraded.

On the other hand, a method (2) is to supply electric current to all ofthe butted portion to be jointed at the same time and has a problem tohave an electric power source in a large capacity which results in ahigh cost. When the joining process is executed with ceramic bodieshaving a complicated shape or asymmetry shape, the electric resistanceand the heat capacity between the electrodes in the butted portion to bejointed are different from a position to a position. Therefore, when allof the butted portion to be jointed are heated by an electric currentflowing to at the same time, a local over-heating occurs to result inthe poor joining property. This limits the shape and the size of theceramic bodies applicable for this joining method. Therefore, it hasbeen long expected to achieve a joining method or an apparatus forjoining the ceramic bodies in a good condition by preventing theproblems such as a poor joining property, a high cost and a poor safetycaused by a movable portion and a simultaneous current supplying of allof the butted portion to be jointed according to the prior art.

An object of the present invention is to improve the conventional abovemethods (A) to (D) wherein the butted portion of the two bodies to bejointed, at least one of which is a ceramic body, is formed by insertinga joining agent between butted planes (which are two planes to bejointed of the two bodies to be jointed to each other in accordance withthe specification of the present invention), or by inserting anconductive ceramic based inserting member for heating combined withjoining agents into the butted planes to be jointed and the joiningagent is heated with the Joule heat to cause a reaction between thejoining agent and the bodies to be jointed for completion of the joiningprocess and, therefore, is to provide a joining method capable ofjoining bodies to be jointed in a large size or in a complicated shapeby means of a switching manner.

A joining method for joining by carrying out a relative movement betweenthe electrodes and the bodies to be jointed has been previouslypracticed at a constant value of the movement speed and/or a constantvalue of the electric current at all position of the butted portion.When the two ceramic bodies are in a large size or in a complicatedshape or has a thickness of the butted portion in a direction ofsupplying electric current different from position to position alongwith a longitudinal direction (a relative movement direction between thebutted portion and two electrodes) or a long length of the buttedportion to be jointed along with the longitudinal direction, it isdifficult to achieve the joining in a good condition. The reason isconsidered as follows:

(1) Under above condition a heat capacity differs from position toposition at the butted portion to be jointed. When the joining iscarried out at a constant value of electric current or electric powerand a relative movement speed, the joining agent at a position whichmeets to requirements of a good condition can be melt sufficiently. Inconnection with the butted portion to be jointed in a shape shown inFIG. 38 (A), the joining agent can be melt insufficiently at the portionwhere the butted portion to be jointed is in a large thickness in adirection of supplying electric current, and the ceramic body to bejointed decomposes and sublimates portionially at the position where thebutted portion to be jointed is in a short distance in a direction ofsupplying electric current and generates the heat in an excessivelylarge amount. The decomposition and sublimation may sometimes damagesthe ceramic body.

(2) In a case when the butted portion to be jointed is uniform in thethickness in a longitudinal direction and the two ceramic bodies havesimple and the same shapes as each other, the butted portion to bejointed, which is in a large length along with longitudinal direction,is not uniform in the heat diffusion coefficient between the center andthe terminal. This causes the poor joining at the terminals of thebutted portion to be jointed. The heat diffusion coefficient is a ratioof the heat diffusion amount at an arbitrary position to that of astandard position. When a positions of pre-heating means and electrodesare in a relation dependent on each other, the terminals of the buttedportion to be jointed have a large coefficient of heat diffusion whichresults in the generation of the poor joining because the butted portionto be jointed can not be kept all the time in the pre-heating state.

A second object of the present invention is aimed at a joining methodfor joining electrically two ceramic bodies which are different in theheat capacitance and the heat diffusion coefficient from each other bymelting the joining agent under making a relative movement between thebutted portion to be jointed and at least two electrodes. The joiningmethod of the second object is able to join electrically the above ofceramic bodies in a good condition by heating uniformly all of thebutted planes to be jointed at a desired joining temperature.

In an operation to join bodies to be jointed at least one of which is aceramic material by heating electrically, there is a case in which thejoining agent, the inserting member for heating or the ceramic body tobe jointed has a high negative temperature dependence of electricresistance. The case requires an electric power source in a high voltageand a high electric current, that is, in a high electric capacitance.This results in a high cost and a high input power kVA and accordinglyin a decrease in the power efficiency and in a high running cost.

When the ceramic bodies having a poor resistance to thermal shock arejoined, it is necessary to adjust the temperature with a control of anelectric current in a small range at the initial current-flowing stage.In a case of requirement to control the electric current in a wide rangefrom a small value to a large value, as mentioned above, the electricpower source in an unit output type has a difficulty to control exactlyan electric current in a small range. The execution over the difficultyneeds a high cost for the electric power source.

Therefore, in order to achieve a decrease in the cost of the electricpower source, a third object of the present invention is to provide amethod for controlling the output power of an electric power source,which is suitable for joining electrically ceramic bodies in a largesize or in a complicated shape.

The problem mentioned above relates to an electric apparatus. Inaddition, there is the following problem relating to the joiningapparatus for use in joining ceramic bodies in a large size or in acomplicated shape. It has been reported that the method to join ceramicbodies in a large size or in a complicated shape with a local heatingcan be achieved by supplying electric current to the joining agentinserted into the butted portion to be jointed or an electric conductiveceramic body. In a joining method to supply current and heat the joiningagent or ceramic body having an electric conduction at a hightemperature, the butted portion to be jointed is heated with a gas flamein a fixed heat amount in order to provide the joining agent or ceramicbody with the electric conductivity. After a main heating is over, theceramic body is cooled naturally with the flame stifled. Even in such anauxiliary heating with a fixed heat amount, the influence on the thermalshock is small in cases of using a ceramic body in a shape having nosharp corner to generate the concentrated stress, a ceramic body in asmall size or a ceramic body in a higher resistance to the thermal shocksuch as Si₃ N₄ ceramic body. In such cases, there is no problem ofcracking during pre-heating or cooling. However, there is a problem togenerate the crack due to the thermal stress at the initial stage ofpre-heating, when the used ceramic body is a ceramic body in a lowresistance to the thermal shock such as Al₂ O₃, a ceramic body having asharp corner, or a ceramic body in a large size. Further, there is aproblem to generate the crack due to the thermal stress at the initialstage of natural cooling under erasing the gas flame after the mainheating by means of the current supplying there to.

A fourth object of the present invention is to provide a joining methodfor joining bodies to be jointed in a large size or in a complicatedshape to obtain an excellent joint under decreasing the thermal shock.

When two bodies to be jointed are to be joined at a high accuracy, ajoining agent layer 4003 is inserted into the butted planes to bejointed of the two bodies to be jointed 4001 and 4002 and is heated intoa melt and cooled for joining the two bodies to be jointed 4001 and4002. In this case, the two bodies to be jointed 4001 and 4002 are heldwith a ceramic body holding equipment having two clamp jigs 4004 and4005.

The joining agent layer 4003 is prepared by drying the joining agent ina paste form applied to the butted planes to be jointed of the bodies tobe jointed, by forming the joining agent in a sheet form or by cuttingthe sintered joining agent lump into a desired thickness. The mostpreferable way for executing the joining method is that the buttedplanes to be jointed of the two bodies to be jointed are parallel toeach other and the joining layer 4003 is uniform in the thickness. Sucha structure makes it possible to heat uniformly all of the butted planesto be jointed to suppress the decrease in the joint strength and also tojoin accurately the two bodies to be jointed with a straight line (in away to make the axial lines of the two bodies to be jointed coincidentto each other). As a practical matter, it is rather difficult andexpensive to make the thickness of the joint layer 4003 uniform. As aresult, the joint layer 4003 is inclined as a practical matter. With thejoining layer 4003 having the thickness decreased from one side toanother side as shown in FIG. 55 (B) in an enlargement manner, the twobodies to be jointed 4001 and 4002 are joined in a curved line. Evenwhen the joining agent layer 4003 is in a uniform thickness, an use ofinclined planes to be jointed of the bodies to be jointed 4001 and 4002results in the curved joining line as shown in FIG. 55(c).

A fifth object of the present invention is to provide a holding devicefor use in joining two bodies to be jointed at a straight line even whenthe bodies to be jointed have a joining agent layer in a heterogenousthickness but butted planes to be jointed not parallel to each other.Further, the object is to also provide a holding apparatus which is ableto join correctly two bodies to be jointed through the joint layer in auniform thickness by the modification of the non-uniformity duringjoining process even when the two bodies to be jointed are provided withthe joining agent layer having a non-uniform thickness as long as thebutted portion to be jointed are parallel to each other.

In a case of preparing a ceramic pipe joint by joining two ceramicbodies in around pipe form having no flat plane at the outside peripheryin a way that the axial lines of the two ceramic bodies cross to eachother, the ceramic pipe has a butted planes to be jointed in a threedimensional curve at the periphery thereof in a similar way to apreparation of a metal pipe joint. Then the two ceramic bodies arejoined to each other by using a ceramic joining agent to obtain aceramic pipe joint. However, it has been found that it is very difficultto form the ceramic body into a complicated three dimensional shape whencompared with the metal case. Even when the two metal pipes have a largegap at the butted planes to be jointed, a welding material melts andfills the gap. Therefore, there is no problem with the metal pipe.However, when the ceramic pipes are joined to each other to prepare theceramic joint, the butted planes to be jointed must be filled with thejoining agent to satisfy various dimensional sizes. It is difficult toadd additional joining agent during the joining process. Even if the gapcan be filled with the joining agent, the joint is very poor in thestrength. Accordingly, the three dimensional butted planes to be jointedof the bodies to be jointed requires very high accuracy.

A sixth object of the present invention is to provide a joining methodfor preparing, in a simple way, a ceramic pipe joint by joining twobodies to be jointed in a pipe form having no a flat plane on theoutside periphery.

The problem to be solved as mentioned above is a common problem to allof the joining methods for joining electrically the two bodies to bejointed. Especially, in the (A) method is to join the two ceramic bodiesby comprising steps of inserting a joining agent between the buttedplanes to be jointed of the two ceramic bodies, pro-heating the buttedportion composed of the joining agent and a part of the two ceramicbodies adjacent to the joining agent, supplying electric current to thejoining agent and melting the joining agent to react with the twoceramic bodies, in order to obtain the sufficiently high joint strength,it has been clearly necessary to carry out sufficiently the reactionbetween the molten joining agent and the two ceramic bodies and to makethe joint layer as thin as possible. In this method, when the twoceramic bodies are merely lapped to each other, the light ceramic bodiesproduces a problem that the blow holes remain in the joint layer or thejoint portion is inclined and slipt out. On the other hand, the heavyceramic bodies causes the joining agent to be excluded from the buttedplanes to be jointed before the sufficient reaction between the joiningagent and the planes to be jointed of two ceramic bodies. As a result,the butted planes to be jointed is not sufficiently heated and resultsin a poor joining strength. In order to solve these problems, the priorart has reported a method to control the distance between the buttedplanes to be jointed of the two ceramic bodies with a distance controlmechanism or a method to press the two ceramic bodies, in a direction ofjoining the two ceramic bodies, with a pressing mechanism. (JapanesePatent Publication (examined) 1989-225583). As a practical matter, whenthe ceramic body is light, the lapped ceramic bodies during apre-heating stage are pressed, in a direction to join the two ceramicbodies, by using the pressing mechanism. When the ceramic body is heavy,the distance control mechanism manages the upper ceramic body to bepositioned at a given place and the distance between the butted planesof the two ceramic bodies to change to a given distance after thesufficient melting of the joining agent.

The technology described above is to restrict the free movement in theaxis direction of ceramic body during the pre-heating stage.Accordingly, when the pre-heating and the electric heating at the laterstep causes the joining agent, the ceramic bodies to be jointed, a clampjig for holding the ceramic body, the pressing mechanism linked to thejig and the linking portion of the distance control mechanism (linkingbar and holding jig) to expand, the expanding amount is absorbed by thejig system comprising the clamp jig, the pressing mechanism, and thelinking portion of the distance control mechanism. Hence, the jig systemstrains, and the strain amount increases with an increase in the thermalexpansion coefficient of the materials (joining agent, ceramic body, jigand linking portion) and an increase in the size of longitudinal length.The strain due to the thermal expansion causes the jig system to damage.In addition, it is not possible to control exactly the distance controlmechanism without knowing the strain amount. As a result, the distancebetween the planes to be jointed of two ceramic bodies is made smallerbeyond necessity and the molten joining agent is pushed away from theplanes to be jointed. This prevents the continuation of electric heatingand causes the poor joint portion.

A seventh object of the present invention is to provide a joining methodto decrease the effect of the thermal expansion of the ceramic body andjig and to produce a high joint strength at the joint portion betweenthe two ceramic bodies.

The previous method according to 1989-225583 (examined) sets theapparent weight of the ceramic body placed on the upper position to zerowhen the ceramic body placed at the upper position is heavy. Theresultant joint strength depends on the position control and the currentsupplying time. An error in the position control or the adjustment ofthe current supplying time causes a gap between the shrinked joiningagent and the ceramic body placed at the upper position. This results inthe generation of blow holes and a weak joint strength. Accordingly,inorder to achieve the suitable position control, the previous method mustcarry out a lot of preliminary experiments and carry out the complicatedcalculation and control.

A eighth object of the present invention is to provide a method forjoining two ceramic bodies, which is capable of tracing simply andsurely the ceramic body placed at the upper position in accordance withthe thickness variation due to the shrinkage of the molten joiningagent, executing sufficiently the reaction between the molten joiningagent and the two ceramic bodies, making the thickness of the jointlayer as thin as possible and preventing the poor joining due to theexcessive electrical heating.

In the (A) method can be achieved by an electric joining method forjoining two ceramic bodies by applying a joining agent having anelectric conductivity at a high temperature to the butted portion to bejointed of ceramic bodies, pre-heating the butted portion to be jointedwith a gas flame, supplying an electric current to flow through thejoining agent and heating the joining agent by Joule heat for a shorttime to join the two ceramic bodies, there is a problem that the jointformed by a joining agent comprising, as an electric conductivecomponent, fluoride has not a sufficiently high strength. For example,the joining composition reported in the Japanese Patent Publication(examined) 1987-65986 includes fluoride (practically CaF₂) of 70 weight%. The large amount of 70 weight % of CaF₂ is resulted from the ideathat the electric conductive component in a higher amount results in abetter joining because the higher content of the electric conductivecomponent make it possible to blow a stable current through the joiningagent.

However, it has been clarified according to the present inventors thatthe higher amount of fluoride gives the joint strength at a hightemperature a bad effect. For example, the joint strength at 1000° C. isonly 20 MPa when silicon nitride ceramic is joined by using the joiningagent consisting of 70 weight % of calcium fluoride. As a practicalmatter, the strength of 200 MPa at 1000° C. has been desirable.

Therefore, a ninth object of the present invention is to provide ajoining agent to produce a joint characterized by a reproducible andstable formation and the high strength practically usable at a hightemperature when the refractory ceramic such as silicon nitride isjoined by the electric joining method.

Further, a tenth object of the present invention is to provide a joiningagent to produce a joint characterized by a reproducible and stableformation and the high strength practically usable as described abovewhen the refractory oxide ceramic is joined by the electric joiningmethod.

It has been known that the joining agent including especially CaF₂ orNaF produces a good joint characterized by a reproducible and stableformation of the joint layer.

However, the conventional joining agent remains Ca²⁺ or Na⁺ ions at thejoint portion. This causes the degradation of the properties at thejoined joint. For example, in connection with the joint strength, Ca²⁺ion or Na⁺ ion in the joint layer lowers the viscosity of the jointlayer, which results in the decrease in the joint strength at a hightemperature. For example, the joint strength at the joint of Si₃ N₄ceramic bodies decreases appreciably at a temperature higher than 1000°C.

Therefore, a eleventh object of the present invention is to provide aceramic joining agent capable of improving the joining strength and aresistance to the corrosion of the ceramic body having a joint portionused as a structural material.

DISCLOSURE OF THE INVENTION

In order to achieve the above first object, the present inventionclaimed in claim 1 is to provide a method for joining electrically twobodies to be jointed, in which a current-flowing member to be energizedor be supplied with electric current for generating Joule heat iscomposed of at least one of three groups of the bodies to be jointed, ajoining agent and a inserting member for heating. The one member has atleast three electrodes linked thereto at a given interval. The electriccurrent supplying is carried out with at least one pair of electrodesselected in serial from the at least three electrodes in accordance witha given electrode switching pattern to move the current flowing areaalong with the butted portion to be jointed.

It is possible to arrange the at least three electrodes at a equivalentdistance or a different distance in accordance with the shape of thebutted portion to be jointed or the heat capacity of the heating area.

The inserting member for heating is composed of, as a basic material, anelectrically conductive ceramic. It is possible to use, as an insertingmember for heating, an electrically conductive ceramic having aninsulating ceramic layer laminated to one or both surfaces thereof asshown in the Japanese Patent Publication (unexamined) 1989-320273 or(unexamined) 1989-320276.

As the electrically conductive ceramic, there can be examplified of anoxide ceramic such as lanthanum chromite, a nitride ceramic such as TiNand ZrN, a carbide ceramic such as SiC and TiC, a siliside ceramic suchas MoSi₂, a boride ceramic such as TiB₂ and ZrB₂, a composite ceramic ofan insulating ceramic such as Al₂ O₃ and Si₃ N₄ and a electricconductive ceramic such as TiN and ZrN and a composite ceramic of a saidinsulating ceramic and a metal.

There are various kinds of a combination of two bodies to be jointedsuch as a combination of two ceramic bodies in an insulating property, acombination of ceramic bodies having not an electrically conduction atroom temperature but having an electrically conduction at a hightemperature, a combination of ceramic bodies at least one of which iselectrically conductive and a combination of a ceramic body and a metalbody.

It is possible to use any method for supplying electric current to themember to generate Joul heat to heat the joining agent. For example, itis possible to permit the electric current to flow in a paralleldirection or a crossing direction to the butted planes to be jointedfrom at least three electrodes.

An electrode switching pattern can be achieved by any pattern capable ofmoving the current-flowing area along with the butted portion to bejointed. Further, the electrode switching pattern is composed not onlyof one pattern but also of a plurality of electrode switching patternsfrom which a desired pattern is sequentially selected in accordance witha change in the condition of the butted portion to be jointed as shownin claim 2. The change in the condition of the butted portion to bejointed is referred to the change in the condition based on atemperature elevation at the butted portion to be jointed, a decrease inthe electric resistance of the current flowing area or a change in theheat capacitance of the current flowing area.

It is possible to use an electrode switching pattern to carry out thecurrent supplying at the shortest distance at the initial stage of thecurrent supplying and then to increase the current-flowing distance stepby step as specified by claim 3. The step by step method referred toherein includes one step. Further, it is possible to use an electrodeswitching pattern capable of carrying out the current supplying in whichthe previous current flowing area and the next current flowing area areoverlapped partially to each other as specified in claim 4.

It is possible to use an electrode switching pattern to carry out thecurrent supplying under the combination of the following two currentsupplying conditions as specified by claim 5. One (a) of the combinationis that the butted portion to be jointed are uniformly heated bychanging at least one of the electric current or power and the hold timein accordance with the condition at other current supplying position ofthe butted portion to be jointed. Another (b) is to decrease the thermalshock of the bodies to be jointed or to promote the reaction with thejoining agent and the bodies to be jointed by changing at least one ofthe electric current or power and the hold time with the time passage inaccordance with the predetermined temperature control pattern.

It is possible to divide at least three electrodes into a pluralityelectrode groups and to control each of the plurality of electrodegroups in accordance with a given electrode switching pattern and agiven current supplying condition as shown in claim 6, in addition tothe collective control of all of at least three electrodes when thebutted portion to be jointed is in a long size or in a complicatedshape. In this case, the current-flowing distance between the electrodescan be changed with the condition the butted portion to be jointed. Incase of the control for divided electrode groups, each of dividedelectrode groups can be controlled in the electric current with onecurrent supplying control apparatus but can be controlled with anindependent current supplying control apparatus attached to each ofelectrode groups. The control pattern of each of electrode groups isarbitrary.

The joining method according to the present invention is to supplyelectric current to sequentially at least three electrodes linked to theelectrically conductive member and to move the current flowing areaalong with the butted portion to be jointed. Accordingly, the joiningmethod according to the present invention does not require the relativemovement between the electrodes and the bodies to be jointed and needsonly few times of maintenance, which is resulted in a safety operation.A close contact between the electrodes and the current supplying memberpermits the high electric current to flow without the generation of thearc and does not cause the ceramic body to damage or to degrade. Movingthe current flowing area along with the butted portion to be jointedmakes it possible to heat the butted portion to be jointed in a longsize to a desired temperature with an electric power source in a smallcapacity when compared with the conventional method to supply electriccurrent to all of the butted portion to be jointed at the same time.When the two ceramic bodies having a complicated shape or a asymmetryshape are joined to each other, it is possible to heat uniformly everyportion by controlling the current supplying condition in accordancewith the change in the electric resistance between the electrodes andthe heat capacity with the current supplying position. As a result, itis possible to prevent the local over-heating which occurs with theconventional joining method to supply electric current to all of thebutted portion to be jointed at the same time. When the joining iscarried out with the butted portion to be jointed of two ceramic bodiesin a pipe form having a large diameter, in a plate form having a largelength or in a complicated shape or an asymmetry shape, the methodaccording to the present invention is very useful and is able to jointhe two bodies to be jointed by heating uniformly all of the buttedportion to be jointed up to a desired temperature under a suitableheating pattern.

The joining method according to claim 2 is to supply electric currentunder the suitable electrode pattern selected from the plurality ofelectrode switching patterns in accordance with the change in thecondition of the butted portion to be jointed and is able to control thecurrent supplying in a high efficiency and to join easily the bodies tobe jointed having a complicated shape.

When the current-flowing member has an electric resistance decreasingwith an increase in the temperature, the current supplying requires ahigh voltage at the initial current-flowing time because the buttedportion to be jointed are in a low temperature and have a high electricresistance at the initial time. The butted portion to be jointed is in ahigh temperature and then the current flowing areas become to be of alow electric resistance. Accordingly, the current flowing distance areacan be extended with the voltage the same as that of the initial time.In a method of claim 3 of the present invention is to supply electriccurrent to between the shortest distance at the initial time and to usethe longer distance for the current flowing step by step under theelectrode switching pattern, it is possible for an electric power sourcehaving a small capacity to heat the butted portion to be jointed up to adesired temperature.

In a case that the current supplying is carried out in a way that theprevious current flowing area and the next current flowing area areover-lapped partially to each other in accordance with a method of claim4, this method can execute the current supplying under making theelectric resistance of the current flowing area as low as possible whencompared with the case where the current flowing areas are noover-lapped. Accordingly, it is possible to move smoothly the currentflowing area at a small variation in the voltage under suppressing thedecrease in the temperature of the heated area.

The method according to claim 5 can achieve the better joining by acombination of the electrode switching pattern and at least one of thecurrent supplying conditions (a) and (b). An current supplying condition(a) is to make it possible to heat uniformly the butted portion to bejointed when the butted portion to be jointed shows a differenttemperature rising ratio or a different reducing ratio of the electricresistance at the current flowing area from position to position withthe current supplying position in a similar way to that of the case whenthe two bodies to be jointed have a complicated shape. It is possible toheat uniformly the butted portion to be jointed in a high efficiencywithout changing the current-flowing distance due to the change in theselection of the electrode when one of the electric current, electricpower and hold time is changed. For example, the butted portion to bejointed can be heated uniformly by changing the hold time in thefollowing way under making the electrode switching pattern constant: Thehold time at the initial current-flowing time is set to a relativelylong time period. Then, the hold time is set to a short time period atthe stable current flowing time after the reaction of the joining agentand the hold time is set to the time period as short as possible at thefinal stage. Further, the current supplying condition (b) is to changeat least one of the electric current, electric power and hold time withthe time passage in accordance with the predetermined temperaturecontrol pattern (heating speed, holding time for keeping the jointtemperature and cooling speed) and accordingly is to reduce the thermalshock of the bodies to be jointed or to promote the reaction of thejoining agent. The used temperature pattern can be determined by apreliminary experiment.

According to the method claimed in claim 6 wherein at least threeelectrodes are divided into a plurality electrode groups and each of theplurality of electrode groups is controlled in accordance with thecurrent supplying condition of a given electrode switching pattern, thebutted portion to be jointed in a long size or in a complicated shapecan be joined in a high efficiency and heated up to a desiredtemperature in a short time period.

According to the method claimed in claim 7 wherein each of electrodegroups is controlled with independent current supplying controlapparatus, it is relatively easy to control each of electrode groups.

Further, the present invention is to provide a following method in orderto achieve the second object to obtain a good joining condition byheating uniformly all of the butted portion to be jointed at the desiredtemperature even when the bodies to be jointed are in a complicatedshape having a heat capacity and heat diffusion coefficient differentfrom position to position:

The method according to claim 8 is to control an electric energysupplied from the two electrodes to the butted portion to be jointed inaccordance with the heat capacity of the two ceramic bodies at eachposition under consideration of the heat diffusion coefficient in orderto heat uniformly all of the butted portion to be jointed at a desiredtemperature.

When the two ceramic bodies in a rectangular plate form and in sizes thesame as each other are to be joined, the heat generated at each positionbecomes constant at the constant electric current because of a constantthickness of the butted portion to be jointed in a current flowingdirection. However, the heat diffusion coefficient is different betweenthe center portion and the terminal portion. It is necessary to increasethe electric energy per unit area at the terminal portion and decreasethe electric energy with a direction from the terminal to the centerportion.

When the electric energy per unit area supplied from the two electrodesto the butted portion to be jointed is controlled in accordance with theheat capacity at each of position of the butted portion to be jointedunder consideration of the heat diffusion coefficient, it is possible tosupply a suitable electric energy to each portion of the butted portionto be jointed. As a result, the butted portion to be jointed can beuniformly heated at the desired temperature without an excess or a lackof heat to obtain a good joint even when the ceramic bodies are in acomplicated shape or have a long portion to be jointed.

In accordance with the method of claim 9, it is possible to controlsimply the electric energy by changing at least one of the relativemovement speed between the electrodes and the butted portion to bejointed and the electric power supplied to the electrodes or by changingat least one of relative movement speed and the electric currentsupplied to the electrodes.

In a case of necessity of an auxiliary heating, when the electrode forsupplying elecric current is made movable independently from theauxiliary heating means in accordance with the method of claim 10, theelectrode can be positioned near to the butted portion to be jointed andcarry out supplying electric current under executing the auxiliaryheating at the place available for the auxiliary heating.

In order to achieve the third object of the present invention, themethod according to the claim 11 is used.

The method is to employ an output power control method for the electricpower source which is used for joining the ceramic body and whichswitches an output of a high voltage and a low current into an output ofa low voltage and a high current in accordance with either of thepredetermined values of the electric current, voltage and temperaturewhen the current supplying is carried out to at least one of a joiningagent, a inserting member for heating and a ceramic body, at least oneof which have a high negative temperature dependence of electricresistance. This makes it possible to reduce extremely the capacity ofthe electric power source when the ceramic bodies having a high negativetemperature dependence of electric resistance. Further it is possible toprovide, at a low cost, an electric power source capable of controllingexactly an electric current in a small range at the initial stage of thecurrent supplying and an electric current in a large range at the finalstage of joining when the ceramic bodies are in a low resistance to thethermal shock.

The following method can achieve the fourth object to prevent thegeneration of the cracking due to the thermal shock occurring with thebodies to be jointed in large size or in a complicated shape and tooffer the joint in a good condition: The method relates to the threeauxiliary heating methods which are carried out by controlling theplurality of auxiliary heating devices arranged around the buttedportion to be jointed and/or the bodies to be jointed from the timebefore the initiating of the main heating to the time after thetermination of the main heating when the bodies to be jointed one ofwhich is a ceramic one are joined electrically as described in claim 12.One method is to sequentially initiate or terminate differential theplurality of auxiliary heating devices. Another method is to increase ordecrease the distance between the auxiliary heating devices and thebutted portion to be jointed and/or the bodies to be jointed. A thirdmethod is to varies the output energy from the auxiliary heatingdevices. The auxiliary heating can be carried out by increasing ordecreasing gradually the temperature of the butted portion to be jointedand/or the bodies to be jointed by using at least one of the above threemethods.

In such a way to use the auxiliary heating to increase or decreasegradually the butted portion to be jointed and/or the bodies to bejointed, it is possible to lower the temperature gradient at the buttedportion to be jointed and the bodies to be jointed in the pre-heatingprocess before the starting of the main heating and to lower thetemperature gradient at the butted portion to be jointed and the bodiesto be jointed in the cooling process after the termination of the mainheating. As a result, it is possible to reduce the thermal stressgenerated due to the temperature gradient at the ceramic body and thebutted portion to be jointed.

A holding apparatus in the following structure can achieve the fifthobject to join, in a straight line, the bodies to be jointed one ofwhich is a ceramic one.

A holding apparatus according to claim 13 provides a clamp angledisplacing mechanism for displacing the angle of at least one clamp jigin a way to coincide the axes of the two bodies to be jointed to eachother when the joining agent melts in connection with at least one clampjig of the two clamp jigs.

Further, an apparatus according to claim 14 provides a ceramic joiningholding apparatus when two clamp jigs are arranged apart from each otherin a vertical direction. The apparatus manages an upper clamp jig tohold the body to be jointed in a way that the axis of the bodies to bejointed is in a vertical line and provides the lower clamp jig with aclamp angle displacing mechanism which comprises a convex sphere planepositioned at the terminal of a non-clamp side portion of the lowerclamp jig and a housing for supporting movably the convex sphere planewith a concave sphere plane corresponding to the convex sphere plane.The convex sphere plane and the concave sphere plane have a curvaturewhich is determined in a manner that each radius centers of the spheresis positioned at a position where the vertical line and the buttedportion to be jointed cross to each other.

Further, an apparatus according to claim 15 provide a ceramic joiningholding apparatus wherein two clamp jigs are arranged apart from eachother in a vertical direction. The apparatus manages a lower clamp jigto hold the body to be jointed in a way that the axis of the body to bejointed is in a vertical line and provides the upper clamp jig with aclamp angle displacing mechanism which comprises a rotation supportingmember for supporting rotatably the rotation center of the terminal of anon-clamp side portion of the upper clamp jig, a holding member forholding movably the rotation supporting member in a direction crossingthe vertical line and an actuating means for actuating the rotationcenter of the rotation supporting member to be positioned on thevertical line.

Further, an apparatus according to claim 16 provide a holding apparatusfor joining bodies to be jointed wherein two holding jigs consisting ofa clamp jig and a linking jig are arranged apart from each other in ahorizontal direction. The apparatus fixes the linking jig in a way thatthe axis of the body to be jointed is positioned on the horizontal lineand provides the clamp jig with a clamp angle displacing mechanism and ahorizontal holding guide for guiding the two bodies to be jointed in ahorizontal direction when the axes of the bodies to be jointed coincideto each other. The clamp angle displacing mechanism comprises a sphereholder positioned at the terminal of the non-clamp side portion, asphere enveloped in the sphere holder and a sphere pressing member whichis flexible and presses the sphere with a given pressure to the side ofthe sphere holder under being in contact with the sphere and which iscapable of moving the clamp jig in a horizontal direction when thejoining agent melts and solidifies.

Further, an apparatus according to claim 17 provides a holding apparatusfor joining bodies to be jointed wherein a pair of clamp jigs arearranged apart from each other in a horizontal direction. The apparatuscomprises one of the clamp jigs with a clamp angle displacing mechanismin a fix side not to move in a horizontal direction. Another clamp jigis provided with a clamp angle displacing mechanism in a moving side andfurther a horizontal holding guide for guiding the two bodies to bejointed in a horizontal direction when the axes of the bodies to bejointed coincide to each other. The clamp angle displacing mechanism atthe fixed side comprises a sphere holder positioned at the terminal ofthe non-clamp side portion, a sphere enveloped in the sphere holder anda sphere pressing member in contact with the sphere which is flexible.The clamp angle displacing mechanism at the moving side is in the samestructure as that of claim 16.

Accordingly, when the joining agent layer is in a heterogeneousthickness (inclined) or when the butted planes to be jointed areinclined and not parallel to each other even with the uniform thicknessof the joining agent layer, the holding apparatus according to claim 13comprising the clamp angle displacing mechanism is able to displace theangle of at least one clamp jig in a way that the two bodies to bejointed have the axes to coincide to each other. As a result, the twobodies to be jointed can be joined to each other in a straight line.When the two bodies to be jointed have the butted planes parallel toeach other, the joining layer is of an uniform thickness and results inthe highest joining strength.

Further, an apparatus according to claim 14 manages the axes of the twobodies to be jointed to coincide to each other with the help of gravitywhen two clamp jigs are arranged apart from each other in a verticaldirection. When one of the two bodies to be jointed is clamped with theupper clamp jig in a way that the axis of the body to be jointed is in avertical line with the joining agent layer in a non-uniform thickness orwith the butted planes not parallel to each other, another body to bejointed is arranged in a inclined position to the vertical line. Whenthe joining agent is heated to melt, the convex sphere plane positionedat the terminal of the non-clamp side portion moves along with theconcave sphere plane enveloped in the housing to change the axis angleof the lower clamp jig. At the final stage, the axes of the lower clampjig coincides with the vertical line. As a result, the body to bejointed clamped by the lower clamp jig and another body to be jointedclamped by the upper clamp jig have the axes coincident to each otherand then are joined to each other. When the curvatures of the convexsphere plane and the concave sphere plane are determined in such a waythat the radius centers of the convex sphere plane and the concavesphere plane are positioned at the point where the vertical line and thebutt planes of the two bodies to be jointed cross to each other, theaxis of the lower clamp jig can be surely made coincident with thevertical line.

A holding apparatus according to claim 15 comprises the upper clamp jigwith a clamp angle displacing mechanism. In this case, the lower clampjig is fixed in a way that the clamped body to be jointed has the axiscoincident with a vertical line. When the joining agent is heated tomelt, the butted plane of the body to be jointed positioned upwardbecomes free from the locking. The rotation supporting member forsupporting rotatably the upper clamp jig with the actuating force ofactuating means moves to cause the rotation center to be on the verticalline. Then the upper clamp jig rotates around the rotation center of therotation supporting member in a way that the axis comes to be along withthe vertical line with the action of gravity. As a result, the body tobe jointed clamped by the lower clamp jig and another body to be jointedclamped by the upper clamp jig have the axes coincident to each otherand then are joined to each other.

When the clamp jigs clamp the bodies to be jointed in a poor workingsize accuracy, the axis of the clamped bodies to be jointed sometimes donot coincide with the vertical line.

An apparatus according to claim 16 is to make the axes of the two bodiesto be jointed coincident to each other with the action of the gravitywhen two holding members consisting of a pair of clamp jigs are arrangedapart from each other in a horizontal direction. Especially, anapparatus according to claim 16 is very suitable for the body to bejointed in a good working size accuracy. When one of the two holdingmembers is merely fixed, the holding member uses the linking jig inorder to move smoothly one of the two bodies to be jointed at thejoining step. When the joining agent layer is not in a uniformthickness, another body to be jointed having the joining agent appliedthereto is arranged in a inclined position against axis of the one bodyto be jointed. Even when another body to be jointed is inclined, anotherbody to be jointed can be held by rotating the sphere holder positionedat the terminal of another clamp jig at the non-clamp side around thesphere and by bending the flexible sphere pressing member. When thejoining agents heated to melt, the butted plane of another body to bejointed is free from the locking. The rotation function between thesphere holder and the sphere, the action that the sphere pressing memberpermits another clamp jig to move in a horizontal direction and theaction of the gravity causes the terminal positioned above another bodyto be jointed to move downward. Accordingly, another body to be jointedis held with a horizontal holding guide, and hence two bodies to bejointed are joined to each other in a way that the two bodies to bejointed have the axes coincident.

In the holding apparatus according to claim 16, the two bodies to bejointed linked to the linking jig must satisfy a given size accuracy forthe working. On the other hand, the joining apparatus has a clamp angledisplacing mechanism against the clamp jig at the fixing side andaccordingly can join two bodies to be jointed, even if provided with toa poor size working. When both of clamp jigs at the fixing side and themoving side are provided with the clamp angle displacing mechanisms, thetwo bodies to be jointed can be joined to each other in a way that theaxes of the two bodies to be jointed coincide to each other by onlyclamping the two bodies to be jointed in such a way that the buttedportion to be jointed is positioned at the upper area. The operationduring the joining is the same as that of claim 16.

The sixth object of the present invention is to join two ceramic bodieshaving no flat plane at the outside periphery as original shapes andbeing in a large size or in a complicated shape or to prepare easily aceramic pipe joint and can be achieved by the following method inaccordance with claim 18.

A flat plane is formed on the outside periphery of a first ceramic pipeby a flat plane making work and then a through-hole is formed on theflat plane by a hole making work. Next, a joining agent is inserted atbutted planes between the flat plane of the first ceramic pipe and abutted plane of a second ceramic pipe. The first and second ceramicpipes are heated at the butted portion to be jointed having the joiningagent inserted therein to be joined to each other. In such a way, theceramic pipe joint can be prepared. The flat plane making work includesall of working methods known in the prior art such as a grinding method.The joining step can be executed by an electrically joining method or afurnace heating method known in the prior art.

In order to carry out easily the position determining work with thesecond ceramic pipe and not to produce the defective joint, the methodis carried out, in a similar way to that of claim 18, the followingsteps of forming an engagement stair at the terminal of the flat planeside having the through hole and forming an engagement convex portion ata terminal of the butted plane of the second ceramic pipe. Theengagement stair and the engagement convex portion are formed in a sucha way that a gap is formed between the terminal plane of the engagementstair and the terminal plane of engagement convex portion at thematching state between the engagement stair and the engagement convexportion.

When two ceramic bodies are joined by an electric joining method, thesize of the flat plane of the first ceramic body is determined in orderto approach closely a joining torch to the butted portion to be jointedin a similar way to that of claim 19.

Therefore, it is possible to join the first and the second ceramic pipesat the flat planes when the flat plane is formed on the outsideperiphery of the first ceramic pipe as shown in claim 18. The flat planework is simple and achieves a high accuracy when compared with a threedimensional work. Accordingly, it is possible to manufacture the ceramicjoint in a short time, to decrease extremely the size error between thebutted portion to be jointed and to obtain a sufficiently high strength.In addition, it is easy to achieve the position determination of theceramic pipes for the arrangement of the joining agent when theengagement stair is formed at the terminal of the flat plane having thethrough-hole and the engagement convex portion is formed at the terminalwhere the butted plane of the second ceramic pipe is formed. Theengagement stair and the engagement convex portion are formed in a sucha way that a gap is formed between the terminal plane of the engagementstair and the terminal plane of engagement convex portion at thematching state between the engagement stair and the engagement convexportion. In such a case, even when the melting and reaction of thejoining agent causes the volume shrinkage, the distance between thebutted planes to be jointed of the two ceramic pipes can be decreased inaccordance with the shrinkage and accordingly there is no defectivejoint.

Further, when the flat plane is made larger as indicated in claim 19, itis possible to join surely with the electrically joining method becausethe joining torch can be positioned at the best position.

The seventh object of the present invention is to join two ceramicbodies in a large size or in a complicated shape under decreasing theeffect of the thermal expansion of the ceramic body and the jig and toachieve the high strength of the joint and can be achieved by thefollowing structure. An improved method aimed by the present inventioncomprises steps of inserting a joining agent between the butted planesto be jointed of the two ceramic bodies, pre-heating the butted portionto be jointed area comprising the joining agent and the partial of thetwo ceramic bodies at the vicinity of the joining agent layer, supplyingcurrent to the butted portion to be jointed to melt the joining agentand carrying out the reaction between the molten joining agent and thetwo ceramic bodies. The method is to join the two ceramic bodies byusing a control mechanism comprising at least one of a distance controlmechanism to control the distance between the butted planes to bejointed and pressing mechanism to press the two ceramic bodies in adirection of joining the two ceramic bodies. It is possible to use anycontrol pattern for controlling the ceramic joining by using at leastone of the distance control mechanism and the pressing mechanism. Thejoining method according to the present invention is characterized bythat the two ceramic bodies are not locked in the axis direction of theceramic bodies by the control mechanism until the initiation of thecontrol by the control mechanism.

In order to eliminate surely the effect of the thermal expansion, thejoining method according to claim 21 of the present invention detectswhether or not the joining agent and the two ceramic bodies to bejointed complete the saturation of the thermal expansion. Afterdetection of the saturation of the thermal expansion, the controlmechanism starts controlling the two ceramic bodies to be jointed.

In the joining method according to the present invention, the twoceramic bodies to be jointed are not fixed in an axial direction untilthe control mechanism starts controlling. Therefore, it is prohibitedthat the two ceramic bodies to be jointed are pressed by making thepressing mechanism to be in an operation state. Further, it isprohibited that the distance between the butted planes of the twoceramic bodies to be jointed are adjusted (including the case when thedistance is kept constant) by making the distance control mechanism tobe in an operation state. Accordingly, when the joining agent, the twoceramic bodies and the jig system expand with the thermal expansioncaused by the preheating or the combination of the pre-heating and theheating by the current supplying, the expansion is not actuallysuppressed by the jig system. As a result, the clamp jig and thestructural portion of the control mechanism do not generate the strain.This solves the problem occurring through the generation of the strainin the jig system caused by the expansion.

When the control mechanism starts the operation before the saturation ofthe expansion, the jig system is subjected to the strain in a smalleramount than that caused when the two ceramic bodies are fixed from theinitial stage. Therefore, the joining method according to claim 21 ofthe present invention is to make the effect of the thermal expansion aslow as possible by measuring the saturation of the expansion and bydifferential the control mechanism after the saturation of theexpansion.

The eighth object of the present invention is to follow quickly thevariation due to the shrink of the molten joining agent when two ceramicbodies in a large size or in a complicated shape are joined to eachother and is achieved by the following method. As described in claim 22,a method for joining two ceramic bodies comprises the following stepsof; inserting a joining agent between the butted planes of two ceramicbodies placed in a vertical direction, pre-heating a joint portionconsisting of said joining agent and a portion of said two ceramicbodies at the vicinity of the joint, supplying current to said buttedportion to melt said joining agent, moving downward the ceramic bodyplaced at the upper position with the weight itself and an external loadto be loaded to said two ceramic bodies, and joining the two ceramicbodies. When the ceramic body placed at the upper position has arelatively small weight (including the weight of jig system), the methodmentioned above can decrease the distance between the butted planes tobe jointed of two ceramic bodies in accordance with the shrinkage of themolten joining agent and in a way to prevent the generation of the blowholes.

When the two ceramic bodies are heavy, the method according to thepresent invention makes it possible to achieve the excellent joint layerby balancing the weight of the ceramic body placed at the upper positionand a portion of the external load with a given balance load totransform the weight of the ceramic body and the load of the jig systeminto a small load. As a result, the apparent weight of the ceramic bodyplaced at the upper position is decreased. The "external load" referredto here is a sum of the weight to be loaded on the upper ceramic whichis consisting of a portion of the weight of clamp jig for holding theceramic body and a portion of the weight of the mechanism linked to theclamp. The "balance load" is a load to be subtracted from the sum of theweight of the ceramic body placed at the upper position and the externalload. The balance load can be realized by providing the ceramic bodyplaced at the upper position and the jig system with an upward force(equivalent to the balance load) smaller than the sum of the weight ofthe ceramic body and the external load. The mechanism for making thebalance load can be achieved by any arbitrary method practicallyavailable.

The method according to claim 23 of the present invention is to pressthe ceramic body placed at the upper position against the ceramic bodyplaced at the lower position after the ceramic body placed at the upperposition is moved down to a given position.

The method according to claim 24 of the present invention is toterminate the current supplying upon detection of the saturation of thedisplacement amount by detecting the displacement amount afterinitiation of the current supplying.

The method according to the present invention can decrease the apparentweight of the ceramic body placed at the upper position by balancing theweight of the ceramic body and the external load with the balance loadeven when the ceramic body placed at the upper position and the externalload is heavy. In a joining method to move downward the ceramic bodyplaced at the upper position by the gravity action, it is possible tomove downward the ceramic body placed at the upper position inaccordance with the shrinkage of the molten joining agent underexecuting the reaction between the molten joining agent and the twoceramic bodies only by changing the balance load in accordance with theweight of the ceramic body placed at the upper position. A simplepreliminary experiment can determine the apparent weight of the ceramicbody placed at the upper position and the external load. It is possibleto determine the apparent weight as a load per unit area. The jointlayer having a sufficiently high strength can be obtained with the twoceramic bodies having various weights and various areas to be jointedwithout doing many preliminary experiments. When the apparent weight ofthe ceramic body placed at the upper position is made low, it is notnecessary to carry out a precise adjustment of the current supplying orelectrically heating time.

In the method according to claim 23, which comprises to press theceramic body placed at the upper position against the ceramic bodyplaced at the lower position at the final joining step, it is capable ofexpelling the gas included in the joint layer to form the joint layer ina high density and of correcting the inclined plane between the twoceramic bodies at the upper and lower positions.

The method according to claim 24 of the present invention is to preventthe excessive electric current supplying and to terminate to supplyelectric current upon detection of the saturation of the displacementamount by detecting the displacement amount after initiation of currentsupplying. The saturated displacement amount after current supplyingmeans that the joining agent reacts sufficiently with the two ceramicbodies to be jointed to decrease sufficiently the thickness of jointlayer. The further current supplying after the saturated displacementamount causes the excessive electric current supplying, although it isdifferent due to the condition which makes the temperature of the buttedportion higher than the necessary value. As a result, the ceramicmaterial at the butted portion is portionially decomposed to form blowholes at the joint layer, which results in the defective joint. Themethod according to claim 24 of the present invention terminates thecurrent supplying in accordance with the saturated displacement amountand is free from the problem in this kind.

The ninth object of the present invention is to provide a joining agentsuitable for use in the electric joining method with the silicon nitrideceramic. The joining agent comprises, as a basic component, CaF₂ of 10to 40 weight %, and the residual of SiO₂ and as an additives, at leastone element of Al₂ O₃ more than 10 weight % Y₂ O₃ of 10 to 55 weight %and Si₃ N₄ of 15 to 45 weight %.

In the above joining agent, CaF₂ more than 40 weight % makes the joiningstrength lower at a high temperature and CaF₂ less than 10 weight %makes the electric conductivity lower and causes the defective joint.

An use of aluminum oxide results in the following function: Alincorporated with Ca in the joint layer suppresses the action of Ca at ahigh temperature and increases the viscosity of the joint layer(softening temperature) to elevate the joining strength at a hightemperature.

The minimum content of Al₂ O₃ is more than 10 weight %. The content ofAl₂ O₃ less than 10 weight % can not achieve the above functionmentioned above and decreases the joining strength at a hightemperature.

The addition of silica SiO₂ is to promote the wetability to the ceramicsand elevates the joining strength at room temperature and a hightemperature when compared with a case having only Al₂ O₃ incorporated.The decrease in the amount of CaF₂ can be compensated by the addition ofSiO₂ in a similar way to the addition of Al₂ O₃.

The incorporated Y₂ O₃ enters the net work structure of silicate(silicate glass) at the joint layer and promotes the elastic coefficientat the joint layer. As a result, the joining agent with Y₂ O₃incorporated increases the joining strength over the joining agentwithout Y₂ O₃. The higher amount of the additive Y₂ O₃ does not resultsin the higher strength of the joint layer. An excess of Y element entersthe joint layer (silicate glass) and destroys the net work structure ofsilicate to decrease the softening temperature, which is results in thedecrease in the joining strength at a high temperature. The additive Yelement reacts with the other component of the joining agent to increasethe joint strength but the effect can be achieved by an addition of Y₂O₃ of 10 to 55 weight %.

The addition of Si₃ N₄ makes the joint layer oxynitride and changes thethermal expansion coefficient close to that of the mother material andelevates the elastic coefficient. Accordingly, the strength at the jointlayer is elevated at room temperature and at a high temperature. As aresult, the joining agent with the additive Si₃ N₄ increases the jointstrength over that without additive Si₃ N₄. An increase in the additiveSi₃ N₄ is not in a regular relation with the increase in the jointstrength. An excess of additives makes the electric conductivity poorand results in the poor joint layer. The material of Si₃ N₄ is verystable but the additive content is 15 to 45 weight %.

The tenth object of the present invention is to provide a joining agentof an oxide system and can be achieved by composition including NaF of 5to 20 weight %, SiO₂ of 30 to 70 weight % and the residual of oneelement selected from the group consisting of Al₂ O₃, TiO₂, Y₂ O₃ andMgO.

This joining agent is based on NaF. The joining agent including NaF morethan 20 weight % lowers the joint strength at a high temperature and thejoining agent including NaF less than 5 weight % makes the electriccurrent flow poor and results in the defective joint.

The addition of SiO₂ promotes the wetability to the ceramic and alsocompensates the decreased amount of NaF.

The incorporation of Al₂ O₃ with Na element can repair the net work(silicate glass structure) having a non-bridging oxygen formed thereinby Na element and elevate the softening temperature of the joint layer.Accordingly, the strength of the joint layer at a high temperature canbe elevated.

The ingredient of MgO is a component for the electric conduction and canelevate the electric conductivity without increasing the amount of NaFand make the glass structure stronger at the range of 2.5 to 10 weight%. As a result, the joint strength at room temperature and a hightemperature is made higher.

The additive Y₂ O₃ enters the silicate net work structure at the jointlayer (silicate glass) and permits the joint layer to have a higherelastic coefficient. Accordingly, the joint strength is made strongerthan that of the joint without Y₂ O₃.

TiO₂ has the same effect as Y₂ O₃.

Further, the eleventh object of the present invention is achieved by thefollowing composition: The joining agent includes, as fluorideadditives, III A group fluoride ScF₃ or YF₃ and achieves the higherstrength at a high temperature. The composition is the III A groupfluoride more than 15 weight % and the residual of at least one elementselected from the group consisting of Al₂ O₃ and SiO₂.

The reason for limiting the III A group fluoride more than 15 weight %is that the joining agent having the III A group fluoride less than 15weight % is in a high electric resistance and does not permit theelectric current to flow. Even when the electric current flows, thegeneration of Joule heat is not uniform. Accordingly, the portion to bejointed melt portionially and result in the poor properties.

The joining agent including at least one element selected from the groupconsisting of Al₂ O₃ and SiO₂ having a high wetability with the ceramicimproves the wetability with the ceramic and results in the superiorjoint.

A composition of 100 weight % of the III A group fluoride ScF₃, or YF₃can achieve the superior joint. The reason is that when the Si₃ N₄ceramic is joined, the joining agent catches SiO₂ produced by aoxidizing reaction of the mother material and a promoting agent for thesintering of the mother material and accordingly improves thewetability.

The joint achieved by the joining agent according to the presentinvention is improved in the joint strength, especially the strength ata high temperature and the corrosion resistance in the following reason:When a comparison is made between the III A group element (Y, and Sc)obtained from the III A group fluoride (ScF₃, or YF₃) and group of (Caor Na) obtained from CaF₂ or NaF, Sc³⁺ ion, Y³⁺ ion, Ca²⁺ ion or Na⁺ iondestroys the Si-O net work structure in the joint layer and enters thenet work structure as a net work modifying ion. The glass having Sc³⁺,or Y³⁺ ion incorporated therein is superior in the various properties tothe glass having Ca²⁺, or Na⁺ ion incorporated therein.

The higher joint strength comes from the higher packing density of theglass at the joint layer, which makes the strain ratio of glass smallerto improve the Young coefficient. Further, the higher strength at a hightemperature results from the reason that Sc or Y ion has a strongerbonding force with oxygen and improves the softening temperature, thatis, the viscosity at a high temperature.

Next, the description is directed to a reason why the joining agentaccording to the present invention improves the corrosion resistanceagainst acid and alkali solution. The corrosion by the acid solution iscarried out by exchanging between H⁺ ion or H₃ O⁺ ion in the corrosivesolution and the modifying ions in the net work of glass. Accordingly,Sc³⁺ ion, or Y³⁺ ion has a stronger bonding force with oxygen than Ca²⁺ion or Na⁺ ion and makes it difficult to be exchanged with H⁺ ion or H₃O⁺ ion. This results in the improvement of the corrosion resistance. Thecorrosion with the alkali solution is carried out by destroying thebonding Si-O in the net work in glass with OH⁻ ion in the corrosionsolution. The glass having Sc³⁺ ion or Y³⁺ ion incorporated thereinincreases the packing density and suppresses the diffusion of OH⁻ ionand improves the corrosion resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (A) and FIG. 1 (B) are a front view and a top view of a joiningapparatus practicing the joining method according to the presentinvention, respectively.

FIG. 2 (A) and FIG. 2 (B) are a table showing an electric power controlpattern used in the first embodiment and a graph showing an electrodeswitching pattern, respectively.

FIG. 3 (A) is a top view showing an arrangement of electrodes, and FIG.3 (B) is a table showing an electrode switching pattern used in secondembodiment.

FIG. 4 is a top view showing an arrangement of electrodes obtained withthe third embodiment.

FIG. 5 is a table showing an electrode switching pattern used in thethird embodiment.

FIG. 6 (A) and FIG. 6 (B) are a cross sectional horizontal view and across sectional vertical view of another joining apparatus of the fourthembodiment, respectively.

FIG. 7 is a top view showing an arrangement of electrodes used in thefifth embodiment.

FIG. 8 is a table showing an electrode switching pattern used in FIG. 7.

FIG. 9 is a top view showing an arrangement of electrodes which is usedin the 6th embodiment and which is obtained by enlarging that of the 5thembodiment.

FIG. 10 is a table showing an electrode switching pattern used in thesixth embodiment.

FIG. 11 is a table showing another electrode switching pattern used inthe sixth embodiment.

FIG. 12 is a table showing further another electrode switching patternused in the sixth embodiment.

FIG. 13 is a table showing another electrode switching pattern used inthe sixth embodiment.

FIG. 14 (A) is a top view showing the arrangement of electrodes for usein the seventh embodiment and FIG. 14 (B) is a cross sectional view of ajoining apparatus practicing the joining method according to the presentinvention. FIG. 14 (C) is a table showing an electric power controlpattern for use in the seventh embodiment.

FIG. 15 (A) is a top view showing the arrangement of electrodes for usein the eighth embodiment and FIG. 15 (B) is a cross sectional view of ajoining apparatus practicing the joining method according to the presentinvention. FIG. 16 is a table showing a temperature control pattern foruse in the eighth embodiment.

FIG. 17 is a table showing an electrode switching pattern used in theeighth embodiment shown in FIG. 16.

FIG. 18 (A) is a perspective view of two ceramic bodies used in theninth embodiment, FIG. 18 (B) is a table showing a temperature controlpattern for use in the ninth embodiment and FIG. 18 (C) is a tableshowing an electrode switching pattern used in the ninth embodiment.

FIG. 19 is a plane view of a joining apparatus for practicing the tenthembodiment.

FIG. 20 is a top view showing an arrangement of electrodes used in thetenth embodiment, and FIG. 21 is a table showing an electrode switchingpattern used in the tenth embodiment.

FIG. 22 is a top view showing an arrangement of electrodes used in theeleventh embodiment, and FIG. 23 is a table showing an electrodeswitching pattern used in the eleventh embodiment.

FIG. 24 (A) is a front view of two ceramic bodies used in the 12thembodiment, and FIG. 24 (B) is a plane view of that of FIG. 24 (A).

FIG. 25 is a table showing an electrode switching pattern used in thetwelfth embodiment.

FIG. 26 (A) is a front view of two ceramic bodies used in the thirteenthembodiment, and FIG. 26 (B) is a plane view of that of FIG. 26 (A).

FIG. 27 is a table showing an electrode switching pattern used in thethirteenth embodiment.

FIG. 28 is a plane view of a joining apparatus practicing the fourteenthembodiment and FIG. 29 is a front view of the joining apparatus shown inFIG. 28. FIG. 30 is a graph showing an electrode switching pattern usedin the fourteenth embodiment.

FIG. 31 is a table showing an electrode switching pattern used in the14th embodiment shown in FIG. 28.

FIG. 32 (A) and (B) are a side view and plane view of a joiningapparatus practicing the fifteenth embodiment, respectively, and FIG. 32(C) is a graph showing a temperature control pattern used in thefifteenth embodiment.

FIG. 33 is a table showing an electrode switching pattern applicable forthe fifteenth embodiment shown in FIG. 32.

FIG. 34 (A) and (B) are a perspective view and a side view of twoceramic bodies used in the sixteenth embodiment, respectively, and FIG.35 is a graph showing a temperature control pattern used in thesixteenth embodiment.

FIG. 36 is a table showing an electrode switching pattern applicable forthe sixteenth embodiment shown in FIG. 34.

FIG. 37 is a perspective view of a joining apparatus for practicing theseventeenth embodiment. FIG. 38 (A) is a perspective view of two bodiesto be jointed and FIG. 38 (B) is a graph showing a relationship amongthe heat diffusion coefficient, electric resistance, supplying electricpower and relative moving speed in a relation to the length of bodies tobe jointed.

FIG. 39 is a block diagram of an electric power source for practicingthe eighteenth embodiment.

FIG. 40 is a graph showing the electric current vs voltagecharacteristics of the electric power source of the 18th embodiment.

FIG. 41 is an outline figure showing a joining process applied to thetwentieth embodiment using an electric power source PS according to thepresent invention.

FIG. 42 is an outline figure showing a joining process applied to thenineteenth embodiment.

FIG. 43 is a graph showing the electric current vs voltagecharacteristics.

FIG. 44 (A) and FIG. 44 (B) are a cross sectional top view and a crosssectional front view of a joining apparatus practicing the 21thembodiment, respectively.

FIG. 45 (A) and FIG. 45 (B) are a cross sectional top view and a crosssectional front view of a joining apparatus practicing the 22thembodiment, respectively.

FIG. 46 is a cross sectional top view of a joining apparatus practicingthe 23th embodiment.

FIG. 47 is a structural model view illustrating the joining process whentwo clamp jigs are apart from each other in a vertical direction inorder to practice the 24th embodiment.

FIG. 48 (A) and (B) are structural model views illustrating theoperation of the embodiment of FIG. 47, respectively.

FIG. 49 (A) and (B) are a structural model view illustrating the joiningprocess when two clamp jigs are apart from each other in a verticaldirection in order to practice the 25th embodiment.

FIG. 50 (A) and FIG. 50 (C) are a structural model view illustrating thejoining process when two clamp jigs are apart from each other in avertical direction in order to practice the 26th embodiment. FIG. 50 (B)is a cross sectional view obtained at B--B line of FIG. 50 (A).

FIG. 51 (A) is a structural model view illustrating the joining processwhen two clamp jigs are apart from each other in a horizontal directionin order to practice the 27th embodiment. FIG. 51 (B) is a crosssectional view obtained at B--B line of FIG. 51 (A).

FIG. 52 is a structural model view illustrating the joining process whentwo clamp jigs are apart from each other in a horizontal direction inorder to practice the 28th embodiment.

FIG. 53 (A) and FIG. 53 (B) are a structural model view illustrating twoceramic bodies which are able to be jointed by a joining method of FIG.52.

FIG. 54 is a cross sectional view of two ceramic bodies to be jointedwith the conventional joining method.

FIG. 55 (A) is a cross sectional view of two ceramic bodies to bejointed with a joining agent in a best arrangement. FIG. 55 (B) is across sectional view of two ceramic bodies to be jointed with a joiningagent in an inclined arrangement. FIG. 55 (C) is a cross sectional viewof two ceramic bodies to be jointed with a joining agent in an uniformthickness but not parallel at the terminal portion to each other.

FIG. 56 is an outline drawing of a joining apparatus practicing thejoining method according to the 29-1th embodiment. FIGS. 57 and 58 aregraphs showing the displacement curve which vary with the control mode.FIGS. 59 and 60 are outline drawings showing other joining apparatuspracticing the joining method according to the 29-2th and 29-3thembodiments, respectively.

FIG. 61 is an outline drawing of a joining apparatus practicing thejoining method according to the embodiment 30. FIG. 62 is graphs showingthe displacement curves with a joining method according to theembodiment 30.

FIG. 63 is a side view of a ceramic pipe joint obtained with theembodiment 31. FIG. 64 is a cross sectional view at II--II line of FIG.63. FIG. 65 is a portionial enlargement of FIG. 64.

FIG. 66 is a cross sectional view of a ceramic pipe in a long size.

DETAILED DESCRIPTION OF THE DRAWINGS

The following description will be directed to a embodiment using fourkinds of electrically joining methods.

Embodiment Group 1

FIGS. 1 to 13 are directed to the embodiments in which two bodies to bejointed at least one of which is an electrically conductive material arejointed with a joining agent inserted at butted planes therebetweenunder the electric current flowing in a direction parallel to the buttedplanes. (B method)

Embodiment 1

FIG. 1 (A) and FIG. 1 (B) are a front view and a top view of the joiningapparatus practicing the joining method according to the presentinvention, respectively. Two ceramic bodies in a pipe form are connectedwith butted portion to be jointed and are jointed to each other byarranging electrodes at the periphery around the butted portion to bejointed.

An used ceramic body is, as an electric conductive ceramic, an electricconductive Si₃ N₄ ceramic body 1a (φ60×φ48×100 L) including, as anelectric conductor, TiN or TiC and having an electric resistance of 10⁻²Ω cm and, as an electric insulating ceramic, an insulating Si₃ N₄ceramic body 1b. The butted portion to be jointed of these ceramicbodies are applied with a joining agent 2 comprising Ti active metalsolder. These ceramic bodies are held by holding jigs 3a and 3b underbeing pressed at a suitable pressure(P).

In order to enable the heating electric current to flow through thebutted portion to be jointed, eight electrodes 4a to 4h made of tungstenand being in a cross sectional form similar to the form of the peripheryof the ceramic bodies are brought into a contact to the periphery of theelectric conductive ceramic bodies (1a,1b) along with the butted portionto be jointed. In this case, a conductive carbon paste are between theceramic body (1a) and the electrodes the electrodes 4a to 4h are in afixed state and arranged along the periphery of the ceramic bodies atregular intervals. In order to prevent the heat diffusion from thebutted portion to be jointed, the adiabatic material is provided nearthe periphery of the butted portion to be jointed. Futher, as shown inJapanese Patent unexamined 1989-20273, a reflective plate may beattached to the adiabatic material.

Next, there is explained an current supplying control apparatus 5 shownin FIG. 1 (B). The electrodes 4a to 4h are connected to an electricpower source 52 through switching terminals 51a to 51h of an electrodeswitching member 51. A control member 54 receives a signal from adetection member 53 for detecting the output voltage, electric currentand electric power of the electric power source 52. Further, the controlmember 54 receives a signal from a temperature detector 6 for detectingthe temperature at the butted portion to be jointed. The switchingmember 51 and the electric power source 52 are controlled by the outputsignal from the control member 54 in accordance with the signal of thesededection. A current supplying control apparatus 5 comprises theelectric power source switching member 51, the electric power source 52,the voltage, current and electric power detection member 53 and thecontrol member 54. The electric power source 52 can be in either of ACor DC operation type. The electric power source in a AC type can use anarbitrary frequency. As the temperature detector 6, a radiationpyrometer, a thermo-couple and the like can be used for detecting thetemperature of portion to be jointed and its vicinity.

A joining process is carried out in argon gas and is controlled by anelectric power control pattern as shown in FIG. 2 (A) under mainlysupplying current the electric conductive ceramic body 1a and joiningagent 2. In order to heat uniformly the butted portion to be jointed, asshown by an electrode switching pattern of FIG. 2 (A), the switchingterminals 51a and 51c are operated at a first time to apply the electricvoltage across the electrodes 4a and 4c. Then, at second time to eighthtime the switching terminals 51b-51d, . . . , 51h-51b are sequentiallyoperated under supplying current to the electrodes 4b-4d . . . , 4h-4bto move a current flowing area in a circumferential of butted portion tobe jointed. At a ninth switching time, the electrodes 4a-4c are againsupplied current and then the two of the electrodes the same order asbefore are operated repeatedly. Each of the two electrodes have ancurrent supplying hold time (referred to a hold time hereinafter) of aconstant value of 70 msec during 5 minutes after initiation of thecurrent supplying and 30 msec during 20 min before the termination ofthe current supplying. A switching time between two pairs of electrodesis made nearly 0. This electrode switching pattern makes it possible toelevate the temperature of butted portion to be jointed effectively bymeans of variation of current supplying time and electric power at aconstant distance between selected electrodes to be supplied current.These electric power control pattern and electrode switching pattern areinput in advance in the control member 54 of the current supplyingcontrol apparatus 5 to be automatically controlled.

The joining apparatus according to this embodiment further comprises adisplay member 55 and a recording member 56. The display member 55displays the voltage, current and the electric power detected at theoutput detector 53 and the temperature detected at the temperaturedetector 6. The recording member 56 records the time passage of the datafrom the output detector 53 and the temperature detector 6. It ispossible to control manually the current and the electric power underwatching the data displayed on the display member 55 with an operationbutton of the control member 54.

The butted portion to be jointed is heated electrically up to atemperature of about 920° C. for 5 min to execute the reaction betweenthe joining agent and the ceramic bodies and is cooled to a roomtemperature in accordance with the electric power control pattern tocomplete the joining.

A gas tight test with the sample so obtained indicates the high gastight degree which can not be detected by the helium leakage detector.The observation of the cross sectional plane of the joint indicates thatthe joint is in a very fine and is very superior. For a comparison, asample in the same shape as that of the above embodiment is prepared byjoining the ceramic bodies by using two electrodes facing to each otherunder rotating the ceramic bodies at 100 rpm. During the joiningprocess, the sample shows an arc generation and a cracking. It is notpossible to obtain a good joint.

Embodiment 2

FIG. 3 (A) shows the arrangement of N electrodes in a way to enlarge thestructure of embodiment 1, wherein the N electrodes of 41, 42, 43 . . .4 (N-2), 4 (N-1), 4N are brought into a contact with the periphery ofthe butted portion to be jointed along with the conductive ceramic body1a in a similar way to that of the embodiment 1.

The electrode switching pattern can be obtained with a suitablecombination of four kinds of patterns as shown in FIG. 3 (B). Inconnection with a pattern 1, the current supplying is carried outbetween the two electrodes adjacent to each other, that is, the twoelectrodes having the shortest distance therebetween causes the currentsupplying to move the current flowing area around the butted portion tobe jointed. At a first time the electrodes 41-42 are supplied currentand then at a second time to n time, 42-43, 43-44, . . . 4 (N-1)-4N,4N-41 are consequently energized. After a (N+1) time, an order of theswitching electrodes is repeated in the same way as that of above. Inconnection with a pattern 2 or 3, the current supplying is carried outbetween the two electrodes having other two electrodes insertedtherebetween and accordingly, the current-flowing distance is two timeslarger than that of the pattern 1. As a practical matter, in connectionwith a pattern 2 at a switching time first to n time, the electrodes tobe supplied current are 41-44, 42-45, 43-46, . . . , 4 (N-1)-42, 4N-43,respectively. In connection with a pattern 3, at a switching time firstto n time, the electrodes to be supplied current are 41-44, 43-46,45-48, . . . , 4 (N-3)-4N, 4 (N-1)-42, respectively. The pattern 2 has amore number of the portion at which the previous current flowing areaand the next current flowing area are over-lapped to each other thanthat of the pattern 3. In connection with a pattern 4, the electrodes tobe supplied current are selected at a distance two times larger thanthat of pattern 1 in way that the previous current flowing area does notover-lap to the next current flowing area. As a practical matter, at aswitching time first to n time, the electrodes to be supplied currentare 41-44, 44-47, . . . , 4 (N-4)-4N, 4 N-43, respectively and thenafter (n+1) time, the electrode switching order is repeated in a similarway that of the above example.

The various kinds of patterns other than the above patterns areapplicable for the electrode switching pattern in accordance with theshape and a heat capacity of the butted portion to be jointed of theceramic body. For example, in accordance with a value of outsidediameter or a thickness of the pipe wall, an arbitrary pattern isselected. The current supplying may be carried out in a pattern the sameas from that of the initiation time to that of the termination time.There is a case at which the current supplying may be carried out at thepatterns more than two kinds from the initiation to the termination ofthe current supplying. For example, in connection with the electricconductive ceramic body having an electric resistance in a negativetemperature dependency, the current supplying is set to two electrodehaving the shortest current-flowing distance (pattern 1) at theinitiation time, to make the initial voltage decreased. The electricresistance of the ceramic body decreases with the increase in thetemperature. Hence, the current-flowing distance is increased so as toextend the heating area. This makes it possible to obtain the excellentheating condition with the electric power source having a smallcapacity. Therefore, the current supplying process at the initial timeemploys a pattern 1 and 2 and then may employ the pattern 3 and 4 afterincreased temperature which pormits the previous current flowing areaand the next current flowing area to be over-lapped at the small area.The current supplying can be carried out by using any other patterncombination in accordance with the ceramic characteristic and the sizeof the butted portion to be jointed. For example, the pattern 1 isselected at the initial step, and after the desired time for currentsupplying has passed, the pattern 2 is selected to finish the currentsupplying with two patterns from the initial step to the terminationstep.

In the embodiments 1 and 2, the ceramic body to be jointed can be in anypipe form including the round pipe or in a round column.

Embodiment 3

FIG. 4 shows the arrangement of N outside electrodes in a way to enlargethe structure of the above embodiment. The out side electrodes and theinside electrodes are the same in the number as each other and thecurrent supplying is carried out between the corresponding electrodesbetween the inside electrodes and the outside electrodes. The Nelectrodes of 41, 42, 43 . . . 4 (N-2), 4 (N-1), 4N are brought into acontact with the periphery of the butted portion to be jointed alongwith the conductive ceramic body 1a in a similar way to that of theembodiment 2. The inside electrodes divided into N of 41', 42', 43', . .. 4 (N-2)', 4 (N-1)', 4N' are arranged to face to the outsideelectrodes, respectively. The inside electrodes are spaced from eachother at regular intervals along with the periphery of the buttedportion to be jointed.

The electrode switching pattern comprises various kinds and, forexample, four kinds of patterns as shown in FIG. 5. A pattern 1 has theshortest distance between the inside electrodes and the outsideelectrodes. As a practical mater, at a first time the electrodes 41-41'are supplied current and then at a second time to n time, 42-42',43-43', . . . 4 (N-1)-4(N-1)', 4N-4N' are consequently supplied current.After a (n+1) time, an order of the switching electrodes is repeated inthe same way as that of above. A pattern 2 has a longer current-flowingdistance than the pattern 1. As a practical matter, at a switching timefirst to n time, the electrodes to be supplied current are 41-42',42-43', . . . , 4 (N-1)-4N', 4N-41', respectively. After that, the ordermentioned above is repeated. A pattern 3 caries out the currentsupplying in a way that various current supplying directions cross onone area. As a practical matter, at a switching time first to n time,the electrodes to be supplied current are 41-42', 42-41', 42-43', . . ., 4N-41', 41-4N', respectively. After that, the order mentioned above isrepeated. A pattern 4 is a combination of the patterns 1 and 2. As apractical matter, at a switching time first to n time, the electrodes tobe supplied current are 41-41', 41-42', 42-42', . . . , 4 (N-1)-4N,4N-4N', 4N-41', respectively. After that, the order mentioned above isrepeated. This embodiment uses the outside electrodes and the insideelectrodes in the same number as each other but it is possible to usethe different number between the inside electrodes and the outsideelectrodes.

It is possible to use a pattern to supply electric current to betweenthe outside electrodes or between the inside electrodes instead ofbetween the outside electrode and the inside electrode. For example, theenergized electrodes to be supplied current can be in the followingorder; 41-42, 41'-42', 42-43', 42'-43'. . . , 4 (N-1)-4N, 4(N-1)-4N'.Various kinds of patterns can be applicable in a way mentioned above. Itis possible to supply electric current to with one pattern from theinitial stage to the final stage but to use a plurality of patternssuitable for the characteristics of a current-flowing member.

Embodiment 4

FIG. 6 (A) and FIG. 6 (B) are a horizontal cross sectional view and avertical cross sectional view of the joining apparatus practicing thejoining method according to the present invention, respectively. Twoceramic bodies to be jointed 1a and 1b in a round pipe form areconnected at the internal periphery along with butted portion to bejointed through a electric conductive member 39. The plurality ofelectrodes 4a to 4d are arranged at the outside periphery along with thebutted portion to be jointed. FIG. 6 shows only the electrode switchingmember 51 of the current supplying control apparatus 5 of FIG. 1 (B).

An used ceramic body is, as an electric conductive ceramic, an electricconductive SiC ceramic bodies 1a, and 1b (φ40×φ24×30 L) having anelectric resistance of 10⁻¹ φ cm. The butted portion to be jointed ofthese ceramic bodies are applied with a joining agent 2 comprising Gepowder. These ceramic bodies are held by holding jigs 3a and 3b.

In order to enable the heating electric current to flow through thebutted portion to be jointed, four outside electrodes 4a, 4b, 4c and 4dbeing in a cross sectional form similar to the form of the periphery ofthe ceramic bodies and an inside electric conductive member 39 in around disc form are brought into a contact to the outside periphery ofthe butted portion to be jointed and the inside periphery of the buttedportion to be jointed between the two ceramic bodies 1a and 1b,respectively. The outside periphery and the inside periphery have aconductive carbon paste applied thereto. In this case, the outsideelectrodes are not moved and are in a fixed state. The outsideelectrodes 4a and 4b are arranged in a nearly perpendicular to eachother, and the two outside electrodes 4a and 4c or 4b and 4d are facedto each other. The inside electrical conductive member can be in a formof a donut. The electrode and the switching member are connected by eachconnection between outer electrode 4a and switching terminal 51a of theswitching member 51, between second electrode 4b and second switchingterminal 51b, and between outher electrodes 4c, 4d and the earthterminal 52e.

A joining process is carried out in vacuum by applying the voltage ofabout 36 V through the electric power source 52 to the butted portion tobe jointed between the ceramic bodies. The electric current is made toflow mainly through the butted portion to be jointed of the SiC ceramicbodies. Each of electrodes is provided with a hold time of 1/60 sec. Theswitching terminals 51a to 51b are switched alternatively from eachother at an arbitrary time interval. In such away, the current flowingdirection is switched sequentially in an order 4a→ceramic body→electricconductive member 39→ceramic body 4c, and 4b→ceramic body→4d. As aresult, the current flowing area moves intermittently around the buttedportion to be jointed.

The electric current increases gradually from the initiation of thecurrent flowing and reaches 130 A which makes the joint temperature1200° C. The joint is heated by Joul heat at the temperature of 1200° C.for about 10 min. After the sufficient reaction between the joiningagent and the ceramic bodies, the electric current is graduallydecreased to cool the ceramic bodies to a room temperature. A testpieces in size of 3×4×40 mm is cut from the jointed ceramic bodies andis subjected to a four point bending test. The resultant joint strengthis 120 MPa.

Embodiment 5

FIG. 7 is a plane view showing the arrangement of N plate electrodesattached to two ceramic bodies in a plate form of a long size. The firstN electrodes of 91, 92, 93 . . . 9 (N-2), 9 (N-1), 9N and the second Nelectrodes N of 91', 92', 93', . . . 9 (N-2)', 9 (N-1)', 9N' are broughtinto a contact with the ceramic body 1a (1b) along with the buttedportion to be jointed. The corresponding electrodes such as 91 and 91'are arranged to face to each other. The first or second electrodes arespaced from each other at regular intervals along with the periphery ofthe butted portion to be jointed. In this embodiment, the first and thesecond electrode groups are the same in the number but can be differentfrom each other. The first electrodes group or the second electrodesgroup can be are formed into a one body.

This embodiment can use, as an electrode switching pattern, variouskinds and, for example, four kinds of patterns as showing in FIG. 8. Inconnection with a pattern 1, at a first time the electrodes 91-91' aresupplied current and then at a second time to n time, 92-92', 93-93', .. . 9 (N-1)-9(N-1)', 9N-9N' are consequently supplied current, and thecurrent flowing area is moved to a longitudinal direction. After a (n+1)time, an order of the switching electrodes is repeated in the same wayas that of above. Accordingly, in this pattern, the current flowing areais moved from one end to another end along with the butted portion to bejointed, that is on a proceeding way only. On the other hand, inpatterns 2 to 4, the current flowing area is alternatively moved fromone end to another end and from another end to one end, that is,alternative both ways.

In connection with a pattern 2, the electrodes to be supplied currentare selected in an order the same as that of the pattern 1. Inconnection with a pattern 3, the current-flowing distance is madelonger. At a switching time first to n time, the electrodes to besupplied current are 91-92', 92-93', . . . ,9 (N-1)-9N', 9N-9 (N-1)',and the current flowing area moves on a going way. At a (n+1)th to(2n-2)th, the electrodes to be supplied current are 93-92', 92-91' andthe current flowing area moves a going back way. After (2n-1)th, theelectrode switching order the same as the above is again repeated. Apattern 4 is a combination of the pattern 2 and the pattern 3 and causesthe current supplying in a way to overlap the previous current flowingarea and the next current flowing area at the portionial portion to eachother.

When the ceramic body having the electric resistance decreasing with anincrease in the temperature is joined, it is preferable that the initialstage having a low temperature at the butted portion selects the pattern1 or 4 and then the stage having a high temperature selects the pattern2 or 3. It is also possible to change the current supplying holding timeand electric power and so on during the control time.

Embodiment 6

FIG. 9 shows an embodiment to divide a plurality of electrodes into aplurality of groups and to control the current supplying of each ofgroups with a given electrode switching pattern. This structure can beapplied suitably for following case: When the joining process is carriedout with a large ceramic body having a long joint and a plurality ofceramic bodies each having complicated shape or non-symmetric shape, allof the butted portion to be jointed can not be uniformly heated easy.The ceramic body is divided into a plurality of portion along with thebutted portion to be jointed. Each of the divided portion has aplurality of electrodes attached thereto. Each of electrodes groups iscontrolled with the current supplying control apparatus and all of thebutted portion to be joint is heated and joined by moving the pluralityof current flowing areas at the same time. In this embodiment, theceramic plates having the same shape as each other are provided with theplurality of electrodes in a way to enlarge the arrangement of theelectrodes of the embodiment 5. The plurality of electrodes are dividedinto three groups, G1 to G3. The G1 group consists of a first group anda second group: the first group of N electrodes of 11, 12, . . . , 1Nand the second group of electrodes N of 11', 12', . . . , 1N'. The G2group consists of a third group and a fourth group: the third group of Melectrodes of 21, 22, . . . , 2M and the fourth group of electrodes M of21', 22', . . . , 2M'. The G3 group consists of a fifth group and asixth group: the fifth group of L electrodes of 31, 32, . . . , 3L andthe sixth group of electrodes L of 31', 32', . . . , 3L'. Each of thefirst group to the third group G1-G3 of the electrodes can be formedinto one electrode in a belt form.

This embodiment can use, as an electrode switching pattern, variouskinds of electrode switching patterns. As shown in FIG. 10, in the G1group of the electrodes, at a first time, the electrodes 11-11' aresupplied current and then at a second time to n time, 12-12', 13-13', .. . , 1N-1N' are consequently supplied current. After a (n+1) time, anorder of the switching electrodes is repeated in the same way as that ofabove. In connection with the G2 group of the electrodes, at the firsttime, the electrodes 21-21' are supplied current and at 2 to m time, theelectrodes to be supplied current are 22-22', . . . , 2M-2M'. After(m+1) time, the above electrode switching is repeated in an ordersimilar to the above. In connection with the G3 group of the electrodes,at a first switching time, the electrodes 31-31' are supplied current.After second to L time, 32-32', . . . 3L-3L' are supplied current inthis order. After (L+1) time, the electrode switching order the same asthe above is repeated. Since L<M<N in the number of electrode, the holdtime must be in an order of electrode group G1<G2<G3.

In a case that the butted portion to be jointed is in a simple form andonly in a long size as shown in FIG. 9, it is possible to set thatL=M=N. The butted portion to be jointed can be joined by executing thecurrent supplying control with each of the electrodes groups at the sametime as shown in FIG. 13 by using one current supplying controlapparatus or the current supplying control apparatuses attachedindependently to each of the electrodes groups. However, when the twoceramic bodies in a complicated shape from each other are electricallyjoined to each other, it is desirable to heat uniformly the buttedportion to be jointed by changing the number or the arrangement distanceof each of electrodes groups or by changing the current supplyingcondition with each of the electrode groups in accordance with thevariation in the heat capacity at each position of the butted portion tobe jointed.

In connection with the current supplying switching pattern, when theelectrode groups G1 to G3 have the electrodes the same number as eachother that is, L=M=N, it is possible to move the current flowing area atthe plurality of positions of the butted portion to be jointed by usingthe three current supplying control apparatuses (not shown in thefigure) and carrying out independently the electrode switching with theelectrode groups G1 to G3 in accordance with the electrode switchingpattern shown in FIG. 12. When the three current supplying controlapparatuses 1 to 3 are used, it is possible to move always only onecurrent flowing area along with the butted portion to be jointed withoutmoving the plurality of current flowing areas along with the buttedportion to be jointed under selecting sequentially the electrode groupG1 to G3 and carrying out the electrode switching in a similar way tothe electrode switching pattern shown in FIG. 11.

When a plurality of electrode groups are controlled in the currentsupplying with each of a plurality of current supplying controlapparatuses, it is desirable to select independently the electrodeswitching pattern and the current supplying condition (the electriccurrent, the electric power, the hold time, the temperature control).Further, it is necessary to control the switching of the electrode ofeach of current supplying control apparatuses in a way that a specifiedelectrode is not supplied from the different current supplying controlapparatuses at the same time.

In the above embodiment, the two ceramic bodies in a plate form aresubjected to the current supplying control by dividing a plurality ofelectrodes into a plurality of groups. Two ceramic bodies having anyother shape than the plate form, for example, a pipe form can be joinedin a similar way to that of the above method.

Embodiment Group 2

The following description is directed to a method for joining two bodiesto be jointed having a inserting member for heating insertedtherebetween (C method). An use of the inserting member for heatingmakes it possible to join not only two ceramic bodies but also a ceramicbody and metal body. Even with the joining method using the insertingmen,bet for heating, it is possible to use a basic structure of thecurrent supplying control apparatus and a pressing device shown in FIG.1 (A) and (B). Therefore, the description with the current supplyingcontrol apparatus and the pressing device is omitted. The inserting men,her for heating can be not only of a structure to apply the joiningagent to the butted planes to be jointed of an electrically conductiveceramic bodies but also of a composite structure to apply the insulatingceramic to one or both sides of the electrically conductive ceramic bodyas shown in Japanese Patent Publication (unexamined) 1989-320273 and1989-320276.

Embodiment 7

The present embodiment uses an electrode arrangement to equip eightoutside electrodes 4a to 4h and a one inside electrode 39 as shown inFIG. 14 (A) and (B). Except for the adiabatic material 7 and theinserting member for heating 20, the structure of FIG. 14 is the same asthat of the embodiment shown in FIG. 1 (A) and (B). Therefore, thedescription with these is omitted. In this embodiment, two insulatingceramic bodies in a round pipe are connected to each other at the buttedportion to be jointed through the inserting member for heating 20. Theinserting member for heating 20 has the electrodes 4a to 4h linkedthereto. The two ceramic bodies 1a and 1b are in a size of 50 mm outsidediameter×42 mm inside diameter×100 mm length and are composed of anusual Al₂ O₃ of an insulating property. The inserting member for heatingis in a structure that the electrically conductive Al₂ O₃ oxide which isin a ring form and has an electric resistance of 10⁻³ φ cm and has aglass NaF system solder at the both sides. The electrodes 4 a to 4b and30 are composed of tungsten and are linked closely to the insertingmember for heating 20 through a carbon paste or carbon sheet. Accordingto the experiment to confirm the effect of the embodiment, the currentsupplying is initiated at room temperature in argon gas with thefollowing order of the two electrodes, 4a-39, 4b-39, 4c-39, 4d-39,4e-39, 4f-39, 4g-39, 4h-39. The butted portion to be jointed andvicinity area are heated at a electric power control shown in FIG. 14(C) under switching sequentially the current flowing area. Each of thetwo electrodes are provided with the holding time of 70 msec of aconstant value. The butted portion to be jointed and vicinity area areheated at 1000° C. for 10 min to causes the joining agent to react withthe two ceramic bodies and the electrically conductive ceramic of theinserting member for heating. The resultant joined bodies are subjectedto a gas tight test with a helium leak detector and shows no gasleakage. The joint area is cut to a test piece, polished and thenobserved with a optical microscope. The joint area shows a dense jointedlayer of 20 microns. The whole of the joint area shows a formation of agood joined area.

The present embodiment shows the case at which the switching of theelectrodes pattern and the hold time are made constant. The joining canbe completed by changing the electrode switching pattern and the holdtime when a given time has passed after the initiation of the currentsupplying. The present method is applicable for the bodies to be jointedhaving an other sectional shape such as a rectangular and shape ofexpecting concentric circles which are used in the present embodiment.In the present embodiment, the inside electrode is formed into a onebody, but the outside electrode can be formed into a one body and theinside electrode can be divided into a plurality of electrodes.

Embodiment 8

The present embodiment relates to a case in which two ceramic bodies 1aand 1b which are in a long shape and in an electric conduction arejoined with a inserting member for heating 20 as shown in FIG. 15 (A)showing the arrangement of the electrodes with the butted portion to bejointed and in FIG. 15 (B) showing a joining method. In the experimentfor confirming the effect of the embodiment, the two ceramic bodies arecomposed of electrically conductive Si₃ N₄ having an electric resistanceof 10⁻³ Ω cm and in a size of 10×150×20 mm (the butted plane, 10×150mm). The inserting member for heating 20 is in a sandwich structure thatan electrically conductive Si₃ N₄ 20a in an electric resistance of 10⁻²Ω cm has insulating layers of Si₃ N₄ 20b in an electric resistance ofhigher than 10⁺⁵ Ω cm integrated at both surfaces thereof. The joiningagent 20c is composed of a Ti system matal solder and is insertedbetween a butted plane of the insulating layers 20b and butted planes ofthe two ceramic bodies 1a and 1b. The heating atmosphere is vacuum of10⁻⁵ torr. The current supplying is initiated at room temperature underswitching sequentially the current flowing area as shown in FIG. 17. Thebutted portion to be jointed and vicinity area are heated under atemperature control pattern shown in FIG. 16 at 950° C. for 5 min tocauses the joining agent to react with the two ceramic bodies to bejointed and the inserting member for heating. The resultant joined bodyis cut to a size of 3×4×40 mm and is subjected to a four points bendingtest. The resultant joining strength is about 220 MPa. The joint area iscut to a test piece, polished and then observed with a opticalmicroscope. The joint area shows a fine joined layer of 8 microns. Thewhole of the joint area shows a formation of a good joined area.

This embodiment is directed to a case when two electrically conductiveceramic bodies are joined. However, it is possible for the insertingmember for heating having both insulating layers applied to the bothsurfaces thereof to join a ceramic body and a metal body. In connectionwith the joining of ceramic and metallic bodies, it is preferable toinsert a soft metal or material having an intermediate thermal expansioncoefficient between the metallic body and the inserting member forheating in order to decrease the strain between the metallic body andthe inserting member for heating in view of releasing the residualstrain.

Embodiment 9

The present embodiment is directed to a case to join two ceramic bodies1a and 1b of an insulating Si₃ N₄ ceramic having a complicated shapefrom each other as shown in FIG. 18 (A). The arrangement of theelectrodes is the same as that of embodiment 8 shown in FIG. 15 (A) andcan be omitted. The inserting member for heating is in a sandwichstructure that an electrically conductive Si₃ N₄ ceramic in an electricresistance of 10⁻² Ω cm has a joining agent of CaF₂ system applied tothe both surfaces thereof and is inserted between the two ceramic bodies1a and 1b. The current supplying is carried out automatically in argonatmosphere under a temperature control pattern shown in FIG. 18 (C) byinputting various given value to program. A variation in the hold timewith the current flowing area is resulting from the reason to heat thewhole of butted planes to be jointed as aninformly as possible in viewof the heat content in consideration of heat capacity of the buttedporiton to be jointed. Accordingly, the similar effect can be obtainedwith a change in the electric current or the electric power. As shown inFIG. 18 (B), the butted portion to be jointed is heated at 1450° C. for10 min and than is pressed pressure in a vertical direction of thebutted planes to be jointed and then is cooled to a room temperatureunder the program. The sample piece of 3×4×40 mm is cut from theresultant joined bodies and subjected to a four point bending test. Thetest result shows the joining strength of 280 MPa and proves the goodjoined condition.

Embodiment Group 3

Referring to FIGS. 19 to 23, the description is directed to a case tojoin two ceramic bodies having an electric conduction at a hightemperature but not at room temperature or to use a joining agent havingan electric conduction at a high temperature under an auxiliary heatingapparatus (A method). The prior art describes a method to join twoceramic bodies by heating the butted portion to be jointed with anauxiliary heating apparatus and by heating through the electrodes toreact the joining agent with the ceramic bodies. Therefore, thedescription of the above method is omitted. The embodiment group 3 isessentially the same as that of embodiment groups of 1 and 2 and isdifferent in the use of the auxiliary heating apparatus. The availableauxiliary heating method comprises a gas flame, an electric furnace or alamp heating or the combination of those.

When the current flowing member has a sufficiently high electricconduction at room temperature as shown in the embodiment groups 1 and 2or the embodiment group 4 described later, there can be used an electricpower source having a low voltage and high electric current depending onthe electric conduction degree. In connection with the current flowingmember according to the embodiment group 3 having no sufficiently highelectric conduction at room temperature and requiring an auxiliaryheating apparatus, it is generally necessary to use an electric powersource having a high voltage and a low electric current because of ahigh electric resistance of the current flowing member heated with theauxiliary heating apparatus.

Embodiment 10

The present embodiment is directed to a case to join two ceramic bodiesin a pipe form. FIG. 19 is a outline drawing showing the joiningapparatus according to the embodiment and is similar to that of FIG. 1(A) except for ten gas burners 8 arranged around the butted portion tobe jointed at a given space. FIG. 20 shows the arrangement of theelectrodes for use in the experiment for confirming the effect of theinvention. FIG. 21 shows an electrode switching pattern used in theexperiment. The used two ceramic bodies are in a pipe form of outsidediameter, 60×inside diameter, 44×length, 100 mm and is composed of aninsulating Si₃ N₄ ceramics. The used joining agent is a CaF₂ systemjoining agent. The ten electrodes 40 to 49 linked closely with theoutside periphery of the butted portion to be jointed are made oftungsten. The gas burners 8 as an auxiliary heating apparatus arearranged around the butted portion to be jointed regular intervals (notshown, in drawing). The ten gas burners are arranged to cover the wholeof the butted portion to be jointed with flame.

The butted portion to be jointed is heated with gas flame at about 800°to 900° C. and then is heated with the electric voltage applied acrossthe electrodes. The current supplying process is carried out to becontroled electric power as shown in FIG. 21 in an automatic control byinputting the electric power, the current supplying time, a switchingpattern and a hold time to a program of an current supplying controlapparatus. After the joining time of 12 min, the pressing pressure isapplied to the two ceramic bodies in the axial direction to face the twoceramic bodies to each other. After 15 min, the gas flame is stopped andthe joined ceramic bodies are cooled to room temperature to complete thejoining process. The resultant joined bodies are subjected to a gastight test with a helium leakage detector and shows a gas leakage in alevel below a detectable value. The sample piece of 3×4×40 mm is cutfrom the resultant joined bodies and subjected to a four point bendingtest. The test result shows the joining strength of 300 MPa and provesthe good joint condition.

In connection with the above embodiment, the preferably uniform heatingcan be achieved by changing the hold time, the current supplying passingtime and the electric power with the elapsed time after the initiationof the current flowing. In the above embodiment, the electrode switchingpattern are changed from the following reason: Because the joining agenthas a high electric resistance at the initial stage of the currentflowing, the voltage in a low level is applied across the electrodeshaving the shorter distance therebetween in accordance with theelectrode switching pattern. As the electric resistance of the joiningagent decreases with an increase in the temperature, the voltage isapplied across the electrodes having a longer distance therebetween inaccordance with the electrode switching pattern. This makes it possibleto heat more uniformly the butted portion to be jointed with theelectric power source having a small capacity by heating a wider currentflowing area. In the above embodiment, the hold time is changed from thefollowing reason: Since the joining agent is heated at a low heatingrate due to a large diffusion of heat into the ceramic bodies at theinitial current flowing stage, the longer hold time can heat moresufficiently each of the joint portion. After the temperature rises upsufficiently, the shorter hold time can heat more uniformly the whole ofthe butted portion to be jointed.

In the above embodiment, the current supplying process is carried out ina way to over-lap the previous current flowing area with the nextcurrent flowing area. The reason is that the over-lap process makes thevariation in the electric resistance between the electrodes smaller thanthe non-overlap process. As a result, it is possible to move the stablecurrent flowing area having a small variation in the voltage. Theelectric joining process with the embodiment group 3 requiresfundamentally a high voltage due to a large variation in the electricresistance with the temperature of the current flowing member. In such acase, an use of this electrode switching pattern has a large effect todecrease the capacity of electric power source, to achieve an uniformheating and to improve the safety operation.

It is noted that the joining can be carried out by using a constantvalue of the hold time and a constant electrode switching pattern or byusing any other control pattern in accordance with the condition of thebodies to be jointed, different from the control pattern shown FIG. 21.

Embodiment 11

This embodiment is directed to a case in which a plurality of electrodes4a to 4l arranged around the butted portion to be jointed between thetwo ceramic bodies in a pipe form are divided into a first electrodegroup G1 (electrode 4a to 4g) and a second electrode group G2 (4g to4a). The electrodes of the two electrode groups are controlled in theelectric power with the current supplying control apparatuses 5A and 5B.The auxiliary heating apparatus comprises an electric heating furnace80. FIG. 22 is a top view showing the arrangement of the electrodes foruse in the experiment to confirm the effects and FIG. 23 is a tableshowing the electrode switching pattern and the current supplyingcondition for use in the experiment. Two ceramic bodies for use in theexperiment are pipes in a size of 100 outside diameter×90 insidediameter×30 mm length and are composed of an insulating Si₃ N₄ ceramics.A used joining agent is a CaF₂ system joining agent. Twelve electrodes4a to 4l made of tungsten are arranged around the periphery of thebutted portion to be jointed at a regular intervals. The auxiliaryheating apparatus is constructed from an electric heating furnace 80.The bodies to be jointed and all of electrodes are placed in theauxiliary electric heating furnace and heated to 900° C. with a heater81 and 82. Then a voltage is applied across the electrodes 4a to 4l tostart heating the joining agent. The electric heating furnace 80 is keptin argon gas atmosphere. The current supplying is carried out with thecurrent control. As shown in FIG. 23, in accordance with the electrodeswitching pattern and the current supplying condition, both electrodesselected from the first electrode group G1 and the second electrodegroup G2, respectively are simultaneously supplied current with thecurrent supplying control apparatuses 5A and 5B. In this case, it isnecessary to control the current supplying control apparatuses 5A and 5Bnot to apply the voltage at the same time to the electrodes 4a and 4g ofthe first electrode group G1 and the second electrode group G2. Afterthe joining time of 15 min, the pressing pressure is applied to the twoceramic bodies in the axial direction to face the two ceramic bodies toeach other. Then, the joined ceramic bodies are cooled in accordancewith the current supplying switching pattern. After the stop of thecurrent supplying the heaters 81 and 82 are also stopped to cool theelectric heating furnace 80 to room temperature to complete the joiningprocess. The following is the reason why the electric current is in alarge size at the initial stage and is decreased at the latter stage:The joining agent is heated as quickly as possible to lower the electricresistance of the joining agent and is subjected to a stable currentsupplying process. Next, after the butted portion to be jointed aresufficiently heated and are subjected to a stable current supplying andto be the temperature suitable for reaction, the current is caused todecrease. When the current is kept a large size, the butted portion tobe jointed are over-heated and are resulted in a poor joining condition.The reason for the variation in the distance between the electrodes isresulted from the reason the same as that described in the embodiment10. The evaluation test the same as that with the embodiment 10 showsthe formation of good joining condition. It is noted that the auxiliaryheating can be effected by any available gas flame instead of theelectric heating furnace. In this embodiment, the whole of the bodies tobe jointed are subjected to an auxiliary heating in the electricfurnace. It is possible to use gas flame in place of electric furnace.The bodies to be jointed in a long size can be subjected at the buttedportion vicinity to an auxiliary heating by placing only the buttedportion vicinity in the electric furnace. This is preferable in view ofthe joining cost. The present embodiment is to divide the electrodesinto two groups, but there may be a case to divide the electrodes into aplurality of groups more than two. In addition, the various methodsdescribed with the embodiment 6 are applicable for the present method ofthis embodiment.

The above embodiment groups are coincident with each other in a pointthat the electric current flows through the current flowing member in adirection parallel to the butted planes to be jointed. Therefore, theelectrode switching pattern shown in embodiments 1 to 11 are applicablefor the cases of above embodiment groups 1 to 3.

Embodiment group 4

In the above embodiments, the electric current is permitted to flow in adirection parallel to the butted planes to be jointed between the bodiesto be jointed. The joining method according to the present invention isapplicable for the joining method to permit the electric current to flowin a direction vertical to the butted planes to be jointed from one bodyto be jointed to another body to be jointed (D method). The presentjoining method is divided into two classes one of which uses a insertingmember for heating and another of which uses no inserting member forheating as described in, for example, Japanese Patent Publication(unexamined) 1989-176283. These methods are conventional and hence areomitted in the detailed description. In a method to use the insertingmember for heating, the inserting member for heating has an electricresistance larger than that of the bodies to be jointed and hence isheated convergently to generate a Joule heat. This is a very highefficient joining method. The joining method described with thefollowing embodiments is applicable for a joining process to join twoelectrically conductive ceramic bodies to each other and a electricallyconductive ceramic body with a metallic body.

Embodiment 12

FIGS. 24 (A) and (B) are side view and a plane view of two ceramicbodies 1a and 1b which are in a rectangular forth having a size the sameas to each other and which are combined through a joining agent 2 at thebutted portion to be jointed. In this embodiment, the ceramic body 1ahas electrodes A1 to AN and B1 to aB linked closely to both sidesthereof. The ceramic body 1b has electrodes a1 to aN and b1 to bN linkedclosely to both sides thereof. The electrodes A1 to AN and theelectrodes a1 to aN make up a first electrode group and the electrodesB1 to BN and the electrodes b1 to bN make up a second electrode group.Each of the electrode groups are arranged in a longitudinal direction atregular intervals. In this embodiment, the first electrode group and thesecond electrode group can be supplied current by using various anelectrode switching patterns. FIG. 25 shows an example of an electrodeswitching pattern usable in this embodiment. A pattern 1 is a pattern inwhich the two electrodes show the shortest distance and the currentflowing area moves sequentially from one terminal to another terminalalong with the butted portion to be jointed (a going way). A pattern 2permits the current flowing area to move reciprocally along with thebutted portion to be jointed. A pattern 3 has a current-flowing distancelonger than that of the patterns 1 and 2 and permits the current flowingarea to move reciprocally along with the butted portion to be jointed. Apattern 4 is a combination of the pattern 2 and the pattern 3. The aboveembodiment is directed to a case having no inserting member for heating.It is noted that the above electrode switching pattern can be applicablefor the case having the inserting member for heating.

Embodiment 13

FIGS. 26 (A) and (B) are a side view and a plane view of two ceramicbodies 1a and 1b which are in a wide rectangular form having a size thesame as each other and which are combined through a inserting member forheating 20 having a joining agent applied to both portion thereof at thebutted portion to be jointed. In this embodiment, the ceramic body 1ahas a first array of electrodes A1 to AN, a second array of electrodesB1 to BN and a third array of electrodes C1 to CN linked closely to theupper plane thereof with a pressing pressure. The ceramic body 1b has athird array of electrodes a1 to aN, a fourth array of electrodes b1 tobN (not shown in FIG. 26) and a fifth array of electrodes cl to cN (notshown in FIG. 26) linked closely to the lower plane thereof with apressing pressure. Each of electrodes a1-aN and b1-bN is linked to eachother under a pressing pressure. The electrodes A1 to AN and theelectrodes a1 to aN make up a first electrode group, the electrodes B1to BN and the electrodes b1 to bN make up a second electrode group andthe electrodes C1 to CN and the electrodes c1 to cN make up a thirdelectrode group. The present embodiment uses three groups of electrodesbut it is possible to use a plurality of groups of electrodes more thanthree. Therefore, FIG. 27 shows an example of electrodes switchingpatterns to use m groups of electrodes. It is possible to use anelectrode switching pattern other than those shown in FIG. 27 inaccordance with the width of the ceramic body. In this embodiment, thebody to be jointed has the electrodes attached to both sides thereof ina way that the electrodes number at the both sides are the same to eachother. It is possible to use the electrodes different in the numberbetween both sides. The electrodes attached to one side can be formedinto one body. The present embodiment uses a inserting member forheating but the electrode arrangement according to this embodiment canbe applicable for the case not to use the inserting member for heating.

The current supplying method according the present embodiment is appliedfor the two ceramic bodies in a plate form but can be applicable for twobodies to be jointed in a pipe form or a complicated shape from eachother.

Embodiment 14

This embodiment is an example to confirm an effect of the currentsupplying method applied for two ceramic bodies in a pipe form. FIGS. 28and 29 are a top view and a side view showing an arrangement of 16electrodes made of carbon A1 to A8 and a1 to a8 linked to two ceramicbodies 1a and 1b which are composed of a SiC ceramic body in a pipe formof outside diameter 60×inside diameter 48×length 100 mm and which has anelectric resistance of 10⁻² Ω cm. A Ge-Si system joining agent 2 isinserted into the butted planes to be jointed of the two ceramic bodiesand are held with a holding jigs at a given pressing pressure. It isnecessary to provide a adiabatic material at the vicinity of the buttedportion to be jointed in order to hold the butted portion to be jointedat a high temperature (not showing in FIG. 28). The joining process iscarried out in argon gas atmosphere. The electrodes are arranged atregular intervals at the outside periphery of the ceramic bodies and arelinked to the outside periphery of the ceramic bodies at a positionapart from 50 mm from the butted portion to be jointed. These are carbonpaste between the ceramic bodies and the electrodes. The butted portionto be jointed is heated by applying the voltage to the electrodes atroom temperature. The current supplying process is carried out to becontroled electric power in an automatic control by inputting anelectrode switching pattern, the elapsed time after the currentsupplying, an current supplying hold time and the electric power shownin FIG. 30 to a program. After the joining time of 5 min at the joiningtemperature of 1200° C., the two ceramic bodies are cooled in accordancewith the program to complete the joining process. The resultant joinedbodies are subjected to a gas tight test with a helium leakage detectorand shows a gas leakage in a level below a detectable value. The jointarea is cut to a test piece, polished and then observed with a opticalmicroscope. The joint area shows a uniformly jointed layer. The whole ofthe joint area shows a formation of a good joint area in a high airtight condition.

Embodiment 15

This embodiment is an example to confirm an effect of the currentsupplying method applied for two ceramic bodies in a wide rectangularform. Referring to FIGS. 32 (A) and (B), two ceramic bodies 1a and 1bare in a size of 100×50×10 mm (butted plane to be jointed, 50×100 mm)are composed of an electrically conductive Si₃ N₄ having an electricresistance of 10⁻² Ω cm. A Ti active metal brazing agent 2 is used. Eachof ceramic bodies has eight carbon electrodes A1 to A4 and B1 to B4 anda1 to a4 and b1 to b4 (not shown in FIG. 32) attached to the upper planeand the lower plane thereof, respectively. The electrodes in each group(A1 to A4, B1 to B4, a1 to a4, b1 to b4) are arranged in regularintervals. The electrode has a contact area of 20×20 mm and are closelylinked with the ceramic bodies thorough a carbon paste at a givenpressing pressure. It is necessary to provide an adiabatic material atthe vicinity of the butted portion to be jointed in order to hold thebutted portion to be jointed at a predetermined temperature (not shownin FIG. 32). The joining process is carried out in argon gas atmosphere.The butted portion to be jointed are heated by applying the voltage tothe electrodes at room temperature. The current supplying process iscarried out to be controlled temperature in an automatic control byinputting a temperature, an electrode switching pattern, and an currentsupplying hold time shown in FIGS. 32 (C) and FIG. 33 to a program. Thejoining agent is heated at 900° C. for 5 mit. The sample piece of 3×4×40mm is cut from the resultant joined body and subjected to a four pointbending test. The test result shows the joining strength of 200 MPa andproves the good joint condition. The joint area is cut to a test piece,polished and then observed with a optical microscope. The joint areashows a uniformly joint layer. The whole of the joint area shows aformation of a good jointed area. Embodiment 16

This embodiment is an example to confirm an effect of the currentsupplying method applied for two ceramic bodies in a different shapefrom each other. Referring to FIGS. 34 (A) and (B), two ceramic bodies1a and 1b are in a size shown in FIGS. 34 (A) and (B) and are composedof SiC ceramic having an electric resistance of 10⁻² Ω cm. An insertingmember for heating 20 is composed of a ceramic SiC body having anelectric resistance larger by two figures than that of the ceramicbodies 1a and 1b and has a Ti system joining agent applied to bothbutted planes thereof. A lower electrode is made of carbon and is inclose contact to the whole of lower plane of the ceramic body 1b. Theten upper electrodes A1 to A10 made of carbon are arranged at regularintervals as shown in FIG. 34 and are in close contact with the upperplane of the ceramic body 1a by a pressing pressure by a pressingapparatus (not shown, in FIG. 34). There are carbon paste betweeninserting member for heating and each ceramic bodies. These are cazbonpaste between inserting member for heating and each ceramic bodies. Thejoining process is carried out in vacuum atmosphere. The butted portionto be jointed is heated by applying the voltage to the electrodes atroom temperature. The current supplying process is carried out to becontrolled temperature to be controlled temperature in an automaticcontrol by inputting a temperature, a time, an electrode switchingpattern and an current supplying hold time shown in FIGS. 35 and 36 to aprogram. After the joining time of 5 min at the joining temperature of900° C., the two ceramic bodies are cooled in accordance with theprogram to complete the joining process. The reason why the switchingtime for the electrode is made slow at a projection area of the ceramicbody 1a is that the projection area is prevented from the delay of thetemperature rising due to the large heat capacity for achievement of auniform temperature distribution. The same result as the above can beobtained by making the electric power at the projection area largerunder making the switching time constant. The joint area is cut to atest piece, polished and then observed with a optical microscope. Thejoint area shows a uniformly joint layer. The whole of the joint areashows a formation of a good joint area.

When the joining process is carried out with the electric currentflowing in a direction to cross the butted plane to be jointed, that is,in a direction vertical to the butted plane to be jointed, it ispossible to divide a plurality of electrodes into a plural groups and tosupply electric current to every group with an electrode switchingpattern the same as that of the embodiment 6.

With a joining process between a ceramic body and a metallic body, it ispreferable to insert a soft metal member or an intermediate memberhaving an intermediate value of a thermal expansion coefficient betweenthe ceramic body and the metallic body and to decrease the residualstress for obtaining a good joint.

The electrically conductive ceramic body can be supplied current at roomtemperature not only at this embodiment but also at the embodimentgroups 1 and 2. Hence, the auxiliary heating apparatus is not necessaryfor elevating the electric conduction but is useful for reducing thethermal shock. The auxiliary heating means comprises gas flame, electricfurnace, lamp heating and their combination.

The method according to the present invention is to move the currentflowing area along with the butted portion to be jointed by currentsupplying selectively and sequentially the electrodes more than arelative movement between three. It is not necessary to move theelectrode and the ceramic body to be jointed during the currentsupplying according to the method of the present invention. The methodaccording to the present invention requires movable portion in a smallnumber and a maintenance in few times and is more safety. The closecontact between the electrode and the current-flowing member permits theelectric current to flow without generation of arc and results in adecrease in the damage or degradation of the ceramic bodies to bejointed due to the arc. The method to move the current flowing areaalong with the butted portion to be jointed per,nits the electric powersource in a smaller capacity to heat the butted portion to be jointed ina long size up to a temperature desired when compared with the electricpower source used in the conventional method to heat the whole of thebutted portion to be jointed at the same time. In order to join twoceramic bodies having a different sectional shape or asymmetry shape,the current supplying condition can be controlled with the differencesin the electric resistance between the electrodes and in the heatcapacity for achievement of uniform heating at every portion. This canprevent the overheat at the local place in a different way from theconventional method to heat the whole of the butted portion to bejointed at the same time. Therefore, the method according to the presentinvention is capable of joining effectively two ceramic bodies in alarge pipe form, two ceramic bodies having a long butted portion to bejointed or two ceramic bodies having a different sectional shape orasymmetry shape from each other. These butted portion to be jointeds canbe supplied current in a good condition and heated to a desiredtemperature under a desired heating pattern to complete the joining.

The method according to claim 2 of the present invention is to supplyelectric current to under a suitable electrode switching patternselected from the plurality of electrode switching patterns inaccordance with a variation in the condition of the butted portion to bejointed and to control effectively the current supplying. In addition,the present method has a feature to join easily the two ceramic bodiesin a complicated shape.

The method according to claim 3 of the present invention is to supplyelectric current to the electrodes having the shortest distance at theinitial stage and to use the electrode switching pattern to increasestepwisely the current-flowing distance. This makes it possible todecrease a necessary maximum voltage and to heat the butted portion tobe jointed in a long size to a desired temperature with a electriccurrent in a low level. In addition, this method is superior in thesafety.

The method according to claim 4 of the present invention is to supplyelectric current in a way that the previous current flowing areaover-laps with the next current flowing area. This method makes itpossible to supply electric current at a condition in which the currentflowing area has an electric resistance as low as possible, comparedwith the case having no overlap current flowing area. Hence, this methodhas a feature to permit the current flowing area to move smoothly with aslight variation in the voltage under suppressing the temperaturelowering at the heated portion.

The method according to claim 5 of the present invention is to heatuniformly the butted portion to be jointed without changing thecurrent-flowing distance due to the variation in the selection of theelectrodes and in accordance with an increase in the temperature of thebutted portion to be jointed, a decrease in the electric resistance ofthe current flowing area and a variation in the heat capacity of thecurrent-flowing portion. Further, this method can decrease the thermalshock of the ceramic bodies and control the reaction of the joiningagent with the ceramic bodies.

The method according to claim 6 of the present invention is to classifythe electrodes into a plurality of electrode groups along with thebutted portion to be jointed and to control the current supplyingprocess in accordance with the given electrode switching pattern and agiven current supplying condition in respect to every electrode group.Therefore, it is possible for this method to join effectively twoceramic bodies having a long butted portion to be jointed or acomplicated shape by heating the butted portion to be jointed to adesired temperature in a short time.

The method according to claim 7 of the present invention is to controleach of electrode groups with each of independent current supplyingcontrol apparatus and accordingly has a feature to control, in thecurrent supplying condition, easily each of electrode groups.

Embodiment 17

FIG. 37 is a perspective view of a joining apparatus for practicing thejoining method according to the present invention. Referring to FIG. 37,reference numerals 101 and 102 denote two ceramic bodies to be jointedin a rectangular form. A reference numeral 103 denotes a joining agentin a solid sheet form, the composition of which varies with thematerials of ceramic bodies. The description of the joining agent isdisclosed in the Japanese Patent Publication (examined) 1987-65986 andother publication and is omitted. Reference numerals 104 and 105 denoteclamp jigs for holding the two ceramic bodies 101 and 102 in a verticaldirection. The upper clamp jig 104 is attached with a linking jig orlinking member 106 which is an element of a control mechanism. It isnoted that a holding mechanism for holding movably the linking member106 is omitted in the description. The linking member 106 is driven witha pressing mechanism 107 having a liquid cylinder operated as a drivingsource. The linking member 106 is separated from the diving member (notshown in the drawing) of the pressing mechanism 107. The linking member106 is linked with the driving member when the pressing mechanismexecutes the pressing. It is possible to control the pressing mechanism107 to take either of two states: One state is a pressing state that thepressing mechanism 107 presses the two ceramic bodies 101 and 102thorough the linking member 106 in accordance with the outside command.Another state is a release state that the pressing mechanism 107 doesnot press and permits the linking member to move freely in an axialdirection (a vertical direction).

The lower clamp jig 105 is fixed at a moving carrier 108. The movingcarrier 108 is provided with a motor and a driving mechanism at theinside and also with a position detector including an encoder consistingof a magnetic sensor or optical sensor (not shown in the drawing). Themoving carrier 108 can be moved by an engagement between a pinion 109equipped at a wheel attached to the one side of the moving carrier and alack 110 to guide the pinion 109. The output signal from the positiondetector (not shown in the drawing) attached to the moving carrier 108is inputted to a displacement meter 111 which transforms the data forthe position of the moving carrier 108 into a signal necessary forcalculation control of a controller 112 (information with a positionrelation between the electrodes and the two ceramic bodies to bejointed).

A reference numeral 113 denotes an electric current source to supply theelectric current to two electrodes 114 and 114 for current supplying thejoining agent 103 in accordance with the command from the controller112. A reference numeral 115 denotes a torch for projecting the gasflame as an auxiliary heating means to pre-heat the butted portion to bejointed. In this embodiment, two torches 115 and 115 are arranged in away to envelope the whole of the butted portion to be jointed withflames from the both sides of a longitudinal direction of the buttedportion to be jointed between the two ceramic bodies 101 and 102. Thetwo torches 115 and 115 are fixed to the moving carrier 108 (not shownin the drawing) and is moved with the movement of the moving carrier108. Accordingly, the butted portion to be jointed can be alwaysenveloped with the gas flame. It is noted that the number or theattaching condition of electrodes 114 . . . and the torches 115 . . . isarbitrary. For a purpose of generating a relative movement in alongitudinal direction of the butted portion to be jointed between thetwo ceramic bodies 101 and 102 and the electrodes 114 or the torches115, the present embodiment manages the driving apparatus 116 to send adriving power and a driving command to a motor arranged in the inside ofthe moving carrier 108. The driving apparatus is controlled by thecontroller 112.

The controller 112 controls the electric current supplying apparatus 113or the driving apparatus 116 to change the electric power per unit areato be supplied to every portion along with a longitudinal direction ofthe butted portion to be jointed in accordance with a variation in theheat capacity. A variation in the heat diffusion coefficient and theelectric resistance varies with the shape of two ceramic bodies can beobtained by a theoretical calculation or the preliminary experiment. Asa result, it is possible to determine the electric power W or thecurrent I and the moving rate S (relative moving rate) of the movingcarrier 108. The controller 112 is caused to memory these data and tocontrol.

Referring to FIG. 38 (A) and (B), the description will be directed to acontrolling method by using a controller 112. Referring to FIG. 38 (A),two ceramic bodies 101a and 101b are the same in the width D and thelength L as each other. The ceramic body 101a placed at upper positionhas a height H varing with the longitudinal direction of the buttedportion to be jointed but the ceramic body 101b placed at a lowerposition has a constant height. In this case, the current-flowingdistance (width D) is constant along with the longitudinal direction ofthe butted portion to be jointed. Accordingly, the electric resistancein spite of current-flowing portion is constant. In connection with acase shown in FIG. 38 (A), FIG. 38 (B) shows a variation in the heatdiffusion coefficient μ, a variation in the electric power W at aconstant value of relative moving rate S and a variation in the relativemoving rates at the constant value of the electric power as a functionof the longitudinal length of the ceramic body (horizontal axis). It isnoted heat that the heat diffusion coefficient μ is expressed by 1 ofdiffusion amount at the center of the longitudinal direction (L/2). Theterminal portion of ceramic bodies 101 and 102 at the longitudinaldirection act as a heat radiator and diffuse heat in a large amount.Further, as the ceramic body 101a has a height H increasing with alongitudinal direction, that causes the heat to diffuse toward theheight direction from butted portion and therefore, has a high heatdiffusion coefficient μ. As a result, in the case of FIG. 38 (A), theterminal portion at the longitudinal direction of the butted portion tobe jointed have a large heat diffusion coefficient μ (heat capacity in aindirect meaning). In order to melt sufficiently the joining agent atthe butted portion to be jointed, it is necessary to determine theelectric power to be supplied to every portion under consideration ofthe heat diffusion (heat capacity). The electric power per unit area canbe easily controlled by changing at least one factor of the electriccurrent or electric power and the relative moving rate. With a constantvalue of relative moving rate S, the electric current can be changedwith the pattern shown by the curve W of FIG. 38 (B). With a constantvalue of the electric power W, the relative moving rate can becontrolled with the pattern shown by a broken line S of FIG. 38 (B).

Next, referring to FIG. 37, the description is directed to a method forjoining two ceramic bodies. The two ceramic bodies 101 and 102 shown inFIG. 37 are of a rectangular form in the same size to each other. Avariation in the heat capacity at every portion of the butted portion tobe jointed can be known indirectly with the heat diffusion coefficientin a similar way to that of FIG. 38 (A). In order to make the relativemoving rate constant, it is necessary to enlarge the moving distance ofthe moving carrier 108. Accordingly, the present embodiment is tocontrol the relative moving rate at a constant value of the electricpower W. First, the butted portion to be jointed are pre-heated with thegas flame from the torches 115 . . . The pre-heating continues until thebutted portion to be jointed are heated at, for example, 800° C. Then,the current supplying starts through the electrodes 114. During thecurrent supplying period, the gas flame is projected to the buttedportion to be jointed in order to prevent every portion from loweringdown.

The controller 112 sends the current supplying command to the currentsupplying apparatus 113 and manages the current supplying apparatus 113to start supplying current to the joining agent. At the same time, thecontroller 112 send the command to the driving apparatus 116 to move themoving carrier 108. The moving carrier 108 is controlled in the movingrate with the given moving rate pattern shown in a broken line of FIG.38 (B). In general, the moving carrier 108 carries out reciprocalmovements several times to supply current the joining agent repeatedly.This makes it possible to heat uniformly the whole of the butted portionto be jointed to a desired temperature. After the joining agent meltssufficiently and reacts with the two ceramic bodies 102 and 102, thecontroller 112 manages the current supplying apparatus 113 to stopsupplying current and at the same time, the moving carrier 108 to stop.The stop position of the moving carrier 108 is predetermined in such away that the pressing mechanism 107 can press given pressure the ceramicbody placed at the upper position in a direction toward the ceramic bodyplaced at a lower position. When the moving carrier 108 stops, thecontroller 112 manages the pressing mechanism 107 to press with a givenpressure the ceramic body placed at the upper position against theceramic body placed at the lower position. As a result, the two ceramicbodies are pressed in a direction at which the two ceramic bodies arejoined and then combined at the butted planes to be jointed. The currentsupplying of the butted portion to be jointed can be stopped at any timeafter or before the operation of the pressing mechanism 107 or at thesame time with operation of the pressing mechanism 107. After the twoceramic bodies are pressed by the pressing mechanism 107, the twoceramic bodies are cooled to complete the joining process. When there isno enough room around the butted portion to be jointed, it is preferablethat the torches 115 and the electrodes 114 are independently moved. Insuch a way, the butted portion to be jointed can be heated sufficientlyby the torches in a necessary number and can be supplied current bymoving freely the electrodes 114 even at a narrow place.

In the above embodiment, the auxiliary heating is executed by thetorches 115 but can be carried out by any other method such as anelectric resistance furnace or a halogen lamp. The electric joiningmethod used in this embodiment is carried out by an A method but can becarried out by any other method. When there is no need to consider thethermal stress, it is not necessary to use the auxiliary heating toelevate the electric conduction.

The electric joining method according to the present invention is tocontrol the electric energy supplied from two electrodes to the joiningagent in accordance with the heat capacity or every portion of theceramic bodies in view of the heat radiation. When the two ceramicbodies are in a complicated shape or have a long butted portion to bejointed, this electric joining method achieves an joint in a goodcondition by heating uniformly the whole of the butted portion to bejointed without an excess or a lack of the heat.

It is possible to control easily the electric energy by at least one ofthe relative moving speed and the electric power to be supplied to theelectrodes or at least one of the moving speed and the electric currentto be supplied to the electrodes.

An arrangement that the electrodes can be operated independently on theauxiliary heating means permits the electrodes to supply electriccurrent to the joining agent from a position close to the butted portionto be jointed under pre-heating the butted portion to be jointed withthe auxiliary heating means positioned at a place to permit thepre-heating operation. As a result, it is possible to obtain a goodjoining condition.

Embodiment 18

FIG. 39 is a block diagram of an electric power source relating to thejoining method according to the present invention. Referring to FIG. 39,a reference character S denotes a terminal for the electric powersource, reference numerals 241a and 242a denote a first transformer anda first electric current (voltage) control circuit comprising saturablereactor or semiconductor control elements such as cylystor ortransistor, respectively, for use in a high voltage, a low currentoutput electric source Paand reference numerals 241b and 242b denote asecond transformer and a second electric current (voltage) controlcircuit comprising saturable reactor or semiconductor control elements,respectively, for use in a low voltage, a high current output electricsource Pb.

A reference numeral 206 denotes an electric power source switchingcircuit for switching between the output of the first control circuit242a and the second control circuit 242b. A switching signal generator210 outputs a signal in accordance with the difference between a signalfrom a electric (voltage) current detector 207 for detecting the current(voltage) supplied to the load L of the two ceramic bodies or a signalfrom a temperature detector 208 for detecting the temperature at thebutted portion to be jointed having the load L, for example, a signalfrom a radiation thermometer and a signal from an electric sourcesetting circuit 209. The electric power source switching circuit 206 isswitched by the signal from the switching signal generator 210 inaccordance with the difference between the two signals.

A reference numeral 211 denotes a electric current (voltage) controlsignal generator for controlling a gate circuit, base driving circuitand reactance control circuit for outputting a signal to change theelectric current (voltage) supplied to the load L. The electric current(voltage) control signal generator 211 selects either of a first and asecond heating pattern setting circuit 212a and 212b for use in a highvoltage and low current output electric power source Pa and a highcurrent and a low voltage power source Pb in accordance with the outputsignal from the switching signal generator 210. When the signal is onefrom each of heating pattern setting circuit, for example, when aconstant current control, a constant voltage control and a constanttemperature control are carried out, the control signal generator 211operates with the difference between an electric signal corresponding tothe current, voltage and temperature and the output signal from thecurrent (voltage) detector 207 or a temperature detector 208, the load Lbeing heated based on the desired heating pattern. It is noted that theelectric power source PS is composed of components excluding theelectric power source terminal S, the current (voltage) detector 207,the temperature detector 208 and the load L.

The setting value of the electric power source switching circuit 209 canbe a current value (Is) or voltage (Vs) corresponding to a portionhaving a maximum value of the variation in the voltage--currentcharacteristics shown in FIG. 43 and a current value or voltage valuewhich are minimum in view of the cost. It is necessary to vary thisvalue in accordance with a kind of the two ceramic bodies, the joiningagent and the inserting member for heating to which current is supplied,the joining condition and the joining state.

In a condition that both electric power sources Pa and Pb are in aconstant current characteristic and the additional values are given tothe current supplying starting voltage Vm, the maximum current Im andthe electric current value (Is) and the voltage value (Vs) shown in FIG.43, the electric power source Pa for a high voltage and a low currenthas maximum rated values of voltage Vmm and current Ism and shows avoltage--current characteristic shown in a solid line Da of FIG. 40. Onthe other hand, the electric power source Pb for a low voltage and ahigh current has maximum rated values of voltage Vsm and current Imm andshows a voltage--current characteristic shown in a solid line Db of FIG.40. It is necessary to vary this value in accordance with a kind of thetwo ceramic bodies, the joining agent and the inserting member forheating, the joining condition and the joining state.

The electric power source applicable for the joining method according tothe present invention is an electric power source in a constant voltagecharacteristic or a constant electric power characteristic besides theconventional electric power source in a drooping characteristic or aconstant current down characteristic. As a practical matter, anavailable electric source is an AC electric power source in a commercialfrequency or AC or DC electric power source of variable frequency by aninvertor type.

When a body to be jointed has a load L in a negative temperaturedependence of electric resistance, it is necessary to measure thevoltage--current curve shown in FIG. 43 and determine Vm, Im and (Vs)and (Is). The next step is to prepare two kind of the electric powersource, one is the electric power source Pa for a high voltage and a lowcurrent having maximum rating values of voltage Vmm and the current Ismand the other is the electric power source Pb for low voltage and a highcurrent having maximum rated values of voltage Vsm and current Imm.

After the electric current supplying starts by applying the outputvoltage from the electric power source Pa for a high voltage and a lowcurrent, the electric current increases gradually with a first current(voltage) control circuit 242a in accordance with the heating patternpredetermined with the first heating pattern setting circuit 212a. Onthe other hand, the voltage between the electrodes decreases gradually.

When a value of the electric current or the voltage between theelectrodes detected by a current (voltage) detector 207 reaches thecurrent value Is or the voltage value Vs set by an electric power sourceswitching circuit 209, an electric power source switching circuit 206operates with the output signal from the switching signal generator 210to switch to the electric power source for a low voltage and a highcurrent Pb and also to a second heating pattern setting circuit 212b.

After that, the electric current increases gradually with a secondcurrent (voltage) control circuit 242b in accordance with the heatingpattern predetermined with the second heating pattern setting circuit212b. Then the butted portion to be jointed is heated to a desiredtemperature for a given time and is cooled to room temperature bydecreasing the electric current to complete the joining process.

Embodiment 19

FIG. 42 shows an embodiment in which the electric power source PSaccording to the present invention is applied for the conventionalmethod C. Two ceramic bodies to be jointed 201a and 201b are made of ahigh density SiC ceramic and the inserting member for inserting memberfor heating made of reaction sintering SiC ceramic having Si dippedtherein, which has a high negative temperature dependence of theelectric resistance.

The measurement is first carried out with the voltage--. currentcharacteristic shown in FIG. 43 in advance and is used for thedetermination of Vm, Im and (Vs), (Is). The used electric power sourcefor use in joining process is an invertor type of an electric powersource in a constant current characteristic characterized by that theelectric power source for a high voltage and a low current Pa isdetermined to have the maximum rated values Vmm=250 V, Ism=10 A and theelectric power source for a low voltage and a high current Pb isdetermined to have the maximum rated values Vsm=20 V, Imm=250 A.Accordingly, the capacity of electric power source is 62.5 kVA with theconventional method and is 7.5 kVA with the method according to thepresent invention and the input power kVA is in a reduction rate thesame as that of the capacity of the electric power source.

When the electrodes 205a and 205b are provided with the output voltagefrom the electric power source Pa for a high voltage and a low current,the electric current starts at about 240 V and then increases graduallywith a first current (voltage) control circuit 242a in accordance withthe heating pattern predetermined with the first heating pattern settingcircuit 212a. On the other hand, the voltage between the electrodesdecreases gradually.

When a value of the electric current or the voltage between theelectrodes detected by a current (voltage) detector 207 reaches thecurrent value Is=8 A or the voltage value Vs=15 V set by an electricpower source switching circuit 209, an electric power source switchingcircuit 206 operates with the output signal from the switching signalgenerator 210 to switch to the electric power source for a low voltageand a high current Pb and also to a second heating pattern settingcircuit 212b.

After that, the electric current increases gradually with a secondcurrent (voltage) control circuit 242b in accordance with the heatingpattern predetermined with the second heating pattern setting circuit212b. Then the butted portion to be jointed is heated to a desiredtemperature 1450° C. for 10 min with the current of 230 A and thevoltage of 9 V between the electrodes 205a and 205b and is cooled toroom temperature by decreasing the electric current to complete thejoining process. It is necessary to control the electric current to riseevery 0.1 A in order to prevent the ceramic bodies from the damage dueto the thermal shock in this embodiment.

Embodiment 20

FIG. 41 shows a second embodiment in which the electric power source PSaccording to the present invention is used. Two ceramic bodies to bejointed 201a and 201b are made of a insulating Si₃ N₄ ceramic in a plateform of (50×20×25 mm). A joining agent 203 of a solder including, as amain ingredient, CaF₂ and kolinite is inserted at the butted planes tobe jointed between the two ceramic bodies. The two electrodes 205a and205b faced to each other are linked with the butted portion to bejointed and are connected to an electric power source PS. The joiningagent 203 has a very negative temperature dependence of the electricresistance and is in a non-conduction at room temperature but comes tobe in a conduction at high temperature.

The measurement is first carried out with the voltage--. currentcharacteristics shown in FIG. 43 in advance and is used for thedetermination of Vm, Im and (Vs), (Is). The electric power source forelectric joining is a reactor type of electric power source Pa in adrooping characteristic having the maximum rated values Vmm=3000 V,Ism=200 mA or a sylistor type of electric power source Pb in a constantcurrent characteristic having the maximum rated values Vsm=400 V, Imm=2A. Accordingly, the capacity of electric power source is 6 kVA with theconventional method and is 1.4 kVA as a whole with the method accordingto the present invention and the input power kVA is in a reduction ratethe same as that of the capacity of the electric power source.

The two ceramic bodies 201a and 201b are pre-heated at the buttedportion to be jointed with gas torches (not shown in the drawing) to atemperature of 850° to 900° C. and then the joining agent 203 isincreased in the electric conductivity. By providing the electrodes 205aand 205b with a higher voltage from the electric power source Pa, theelectric current starts at about 2800 V and thereafter increasesgradually with a first current (voltage) control circuit 242a inaccordance with the heating pattern predetermined with the first heatingpattern setting circuit 212a.

When a value of the electric current or the voltage between theelectrodes detected by a current (voltage) detector 207 reaches thecurrent value Is=150 mA or the voltage value Vs=380 V set by an electricpower source switching circuit 209, an electric power source switchingcircuit 206 operates with the output signal from the switching signalgenerator 210 to switch to the electric power source Pb for a lowvoltage and a high current.

After that, the electric current increases gradually with a secondcurrent (voltage) control circuit 242b in accordance with the heatingpattern predetermined with the second heating pattern setting circuit212b. Then the butted portion to be jointed is heated to a desiredtemperature 1700° C. with the current of 1.6 A and the voltage of 370 Vbetween the electrodes 205a and 205b and after 10 min is cooled to roomtemperature by decreasing the electric current to complete the joiningprocess. It is noted that the preheating temperature is decided to bethe above temperature in view of the pre-heating facility, pre-heatingcost and the prevention of the ceramic bodies from degradation.

In the above embodiment, the first and the second transformer 241a and241b are independent from each other but it is possible to use a onetransformer using a common iron core and outputting two powers.

When the voltage vs. current curve is in a high slop at a low currentrange, or when the ceramic body is low in the thermal resistance to thethermal shock, it is possible to use a plurality of the electric powersources for a high voltage and a low current divided the output powermoreover.

In such a way, the joining method according to the present inventionachieves the large amount of the reduction in the facility cost and therunning cost. When a ceramic body having a poor thermal resistance tothe thermal shock is joined, it is possible to prevent the ceramic bodyfrom the damage by using an electric power source in a low cost becausethe temperature control can be easily achieved by the current supplyingcontrol at a low current range.

Embodiment 21

FIGS. 44 (A) and (B) are a top view and a front view of an apparatuspracticing the joining method according to the present invention,respectively. Referring to FIG. 44, reference numerals 301a and 301bdenote two Al₂ O₃ ceramic bodies in a pipe form (φ60×φ55×100 mm length)and have a joining agent 302 inserted at the butted planes to be jointedtherebetween. The two ceramic bodies 301a and 301b with the joiningagent 302 are fixed by fixing jigs 303a and 303b and are rotated with arotating device 304 which rotates with the jig 303b.

Reference numerals 305a, 305b and 306a, 306b denote gas torches forfirst and second systems, respectively and are arranged in a way thatthe heading portion of each of the torches is apart from the buttedportion to be jointed at a distance of 20 mm. The first system of thetorches 305a and 305b are combined with electrodes 308a and 308bconnected to an electric power source 307 into one body. The electrodes308a and 308b are linked or positioned closely, at each of their headingportion, to the butted portion to be jointed.

Reference numeral 309 and 310 denote an inflammable gas cylinder and aburning support gas cylinder, respectively. The gas flow is adjusted bygas flow adjusters 311a, 312a and 311b, 312b. The gas flow adjusters311a, 312a and 311b, 312b are switched to the first and the secondsystems by a system switching control device 320. The above both gasesare mixed together by gas mixers 313a and 313b and are supplied to thefirst system of torches 305a and 305b and the second system of thetorches 306a and 306b.

The torches 305a, 305b and 306a, 306b are controlled in a firing orstopping time, a system switching time, an current supplying startingtime or an current supplying stopping time with a time programpredetermined with a heating pattern or a temperature setting signalfrom a temperature sensor (not shown).

In such a structure, the two ceramic bodies are pre-heated, at thebutted portion to be jointed and its vicinity, with the first system oftorches 305a and 305b fired under being rotated. Propane gas as ainflammable gas and oxygen gas as a burn support gas are caused to flowat rates of 0.4 l/min and 1.0 l/min, respectively. After 5 min, thebutted portion to be jointed are heated to a temperature of about 500°C. and then the second system of torches 306a and 306b are fired tocontinue the pre-heating. The gas flow of the second system is the sameas that of the first system. After 10 min, the butted portion to bejointed are heated to a saturated temperature of 900° C. After that, theelectrodes 308a and 308b are applied with voltage from the electricpower source 307 to supply current to the joining agent 302. The currentis controlled to increase gradually in a way that the joining agentreaches a desired temperature with a control device attached to theelectric power source 307. After the two ceramic bodies are kept for 5min, the current is gradually decreased and finally the electric powersource is stopped. After that, the second system of torches 306a and306b are stopped and after 10 min, the first system of torches 305a and305b are also stopped. The two ceramic bodies are cooled naturally tocomplete the joining process.

The joint part is subjected to a dye penetration test by applying dye tothe joint and observed with an optical microscope. The test resultindicates no cracking at the joint.

Embodiment 22

FIGS. 45 (A) and (B) are a top view and a front view of an apparatuspracticing the joining method according to the present invention,respectively. Referring to FIG. 45, the same structural elements areindicated by the same reference numeral as that of FIG. 44. Referencenumeral 301a and 301b denote two ceramic bodies; a reference numeral 302denotes a joining agent; reference numerals 303a and 303b denote fixingjigs; a reference numeral 304 denotes a rotation device; referencenumerals 306a, 306b, 306c, 306d denote torches; a reference numeral 307denotes an electric power source; reference numerals 308a and 308bdenote electrodes arranged indipendently at the vicinity of the torches306a and 306c; reference numerals 311 and 312 denote gas flow adjustors;a reference numeral 313 denotes a gas mixer for supplying gas to thetorches 306a to 306d.

The different point from the embodiment 21 is that the torches 306a to306d are attached to torch moving devices 314a to 314d, respectively inorder to change the distance between each of the heading portion oftorches and the butted portion to be jointed and to change the movingrate of the torches. These changes are controlled by a position controldevice 321.

The torches 306a to 306d are controlled in a firing or stopping time, asystem switching time, an current supplying starting time or an currentsupplying stopping time with a time program predetermined with a heatingpattern or a temperature setting signal from a temperature sensor in asimilar way to that of Embodiment 21.

In such a structure, the two ceramic bodies are pre-heated, at thebutted portion to be jointed, with the torches 306a to 306d fired at aposition apart from the butted portion to be jointed by 100 mm underbeing rotated. The torches 306a to 306d are moved close to the buttedportion to be jointed at a moving rate of 10 mm/min and then kept at aposition apart from the butted portion to be jointed from 20 mm for 5min. Propane gas and oxygen gas are caused to flow at rates of 0.4 l/minand 1.0 l/min, respectively. The butted portion to be jointed are heatedto a saturation temperature of 900° C. at a heating rate of 60° C./min.After that, the butted portion to be jointed are heated by supplyingcurrent to be electrode in a similar way to that of Embodiment 21 andafter a given time, the electric power source is stopped. The torchesare removed from the butted portion to be jointed at a speed of 10mm/min and then kept at a position apart from the butted portion to bejointed by 100 mm for 5 min. After the flame is erased, the two ceramicbodies are cooled naturally. The observation with the joint indicates nocracking in a similar way to that of Embodiment 21.

Embodiment 23

FIGS. 46 is top view of an apparatus practicing the joining methodaccording to the present invention. Referring to FIG. 46, the samestructural elements are indicated by the same reference numerals as thatof embodiment 22.

The different point from the Embodiment 22 is that the a gas flow ratechanges stepwisely from an increase to a decrease with the time passageby a gas flow control device 322. A position control device controlsuitably the distance between each of the torches 306a to 306d and thebutted portion to be jointed in order to prevent the flame from beingerased by the close approach of the torches to the ceramic bodies.

The torches 306a to 306d are controlled in a firing or stopping time, asystem switching time, an current supplying starting time or an currentsupplying stopping time with a time program predetermined with a heatingpattern or a temperature setting signal from a temperature sensor in asimilar way to that of Embodiment 21.

In such a structure, the two ceramic bodies are pre-heated, at thebutted portion to be jointed, with the torches 306a to 306d fired at aposition apart from the butted portion to be jointed by 20 mm underbeing rotated. Propane gas and oxygen gas gas start to flow at rates of0.1 l/min and 0.25 l/min, respectively and are fired. The flow ratiobetween propane gas and oxygen is controlled to be about 1:2.5. The flowrate of propane gas is increased by 0.1 l/min every 2 min and finallythe flow rates are 0.4 l/min and 1.0 l/min with propane gas and oxygengas, respectively. The butted portion to be jointed are heated with thisgas flow for 5 min to a saturation temperature of about 900° C. Afterthat, the butted portion to be jointed are heated by supplying currentto be electrode in a similar way to that of Embodiment 21 and after agiven time, the electric power source is stopped. The flow ratio betweenpropane gas and oxygen is controlled to be about 1:2.5. The flow rate ofpropane gas is decreased by 0.1 l/min every 2 min and finally the flowrates are 0.1 l/min and 0.25 l/min with propane gas and oxygen gas,respectively. After the ceramic bodies are kept for 2 min at the finalflow rate, the flame is erased. The ceramic bodies are cooled naturallyto complete the joining process. The observation with the jointindicates no cracking in a similar way to that of Embodiment 21.

In the above embodiment, the torches are arranged only around the buttedportion to be jointed. However, it is possible to arrange the torchesany other portion than the butted portion to be jointed, for example, anarea in a longitudinal direction of two ceramic bodies in view of thetemperature distribution in accordance with the size, shape of theceramic bodies. It is possible to use a combination of Embodiments 21 to23. The number of the torches can be arbitrary. It is possible to use astructure to rotate the torches with fixing the two ceramic bodies. Thejoining method according to the present invention is directed to amethod A type but is applicable for any other methods. The presentembodiment uses a gas flame as an auxiliary heating means but it ispossible to any other heating method such as lamp heating or resistorheater. The present joining method is applicable for the case when thejoining is carried out with a ceramic body and a metallic body andfurther applicable for the case when the butted portion to be jointedare heated with laser in a high heat density instead of the electricheating.

In such a way, the joining method according to the present inventionmakes it possible to achieve a joint in a good condition withoutcracking due to the thermal stress at the butted portion to be jointedby using a control device to control the heat amount during thepre-heating time and the cooling time in connection with a joiningprocess by a local heating of ceramic bodies.

Embodiment 24

FIG. 47 is a cross sectional view of a ceramic holding apparatus havingtwo clamp jigs arranged in a vertical direction. This apparatus is usedfor the electric joining method according to the present invention.Referring to FIG. 47, reference numerals 401 and 402 denote two ceramicbodies to be jointed; a reference numeral 403 denotes a joining agent ina sheet form; and reference numerals 404 and 405 denote an upper clampjig and a lower clamp jig, respectively. The two ceramic bodies 401 and402 are in a cross sectional shape of 15 mm square and 20 mm length. Theupper clamp jig 404 has a position adjusting rod 406 attached to the topterminal thereof in order to make the axis of the upper clamp jig 404coincident with a vertical line. The position adjusting rod 406 issupported by a supporting means (not shown in the drawing) and is movedin a vertical direction when the ceramic body 401 is attached to orremoved from the upper clamp jig 404. The position adjusting rod 406 hasa rod driving device (not shown in the drawing) attached to the terminalthereof to adjust a distance between the butted planes of the buttedplanes of the two ceramic bodies to be jointed 401 and 402 when thejoining agent melts. The upper clamp jig 404 can be in any structurecapable of holding the terminal of the ceramic body 401.

The lower clamp jig 405 comprises a clamp body 407 having a concavehousing 407a which has an opening at the upper direction thereof, alower heat insulator 408 put in the concave housing 407a, two adjustingbolts 409 and 410 engaged with the opening end of the clamp body 407 andside heat insulators 411 and 412 fixed at the terminal of the adjustingbolts 409 and 410, respectively. The lower heat insulator 408 is linkedwith the terminal of the ceramic body 402 and supports the two ceramicbodies from an axial direction. The side heat insulators 411 and 412cause the adjusting bolts 409 and 410 to rotate for the positionadjustment and support the ceramic body 402 from the horizontaldirection under being linked with the both facing sides of the ceramicbody 402. These heat insulators 408, 411 and 412 prevent the heat fromdiffusing from the ceramic body 402 to the clamp body 407 when thejoining agent is electrically heated.

The clamp body 407 has a convex spherical plane 413 formed at theno-clamping side terminal thereof and has stoppers 414 and 415 formed atthe side wall thereof into one body. The clamp body 407 is placed into ahousing 417 which has a concave spherical plane 416 corresponding to theconvex spherical plane 413 and supports movably a convex spherical plane413. Boll bearings 418 are arranged between the convex spherical plane413 and the concave spherical plane 416 in order to move the clamp bodysmoothly. It is possible to make the convex spherical plane 413 and theconcave spherical plane 416 from the bearing material instead of usingthe boll bearings 418. The convex spherical plane 413 and the concavespherical plane 416 have a curvature radius R1 and R2, respectively in away that the centers of the convex spherical plane 413 and the concavespherical plane 416 are positioned at a point where a vertical line Xcrosses the butted portion to be jointed (403) between the two ceramicbodies 401 and 402. The housing 417 has fixing stoppers 419 and 420formed in a projection form in accordance with the stoppers 414 and 415.These stoppers have a function to prevent the clamp body 407 fromrotating by an excess amount. Adjustment actuating means 421 and 422composed of springs having the same strength to each other are arrangedbetween the inside wall of the opening of the housing 417 and theoutside wall of the clamp body 407 in order to adjust an initialposition of the clamp body 407 and to suppress the plane rotation of theclamp body 407.

In the above embodiment, a clamp angle position displacement mechanismis composed of the convex spherical plane 413, the concave sphericalplane 416, boll bearings 418 and the housing 417.

Next, the following description is directed to an operation of thisembodiment. When the joining agent 403 is not uniform in the thicknessas shown in FIG. 48 (A), the lower ceramic body to be jointed 402 isarranged in a manner that the axial line X1 inclines against the axialline of the upper ceramic body to be jointed 401, that is, a verticalline X. When the joining agent 403 melts by the electrical heating, thelower clamp jig 405 moves to change the angle of the axial line X1against the vertical line X by means of the gravity force and the actionof the convex spherical plane 413 formed at the opposite side from theclamping side and the concave spherical plane 416 formed in the housing417. Finally, the axial line X1 of the lower clamp jig 405 coincideswith the vertical line X as shown in FIG. 48 (B). As a result, theceramic body 402 clamped by the lower clamp jig 405 comes to be joinedwith ceramic body 401 clamped by the upper clamp jig 404 in a mannerthat the axial line coincident with the axial line of the ceramic body401 clamped by the upper clamp jig 404. When the joining agent 403 meltsand solidifies, the rod driving means (not shown in the drawing)connected to the position adjusting rod 406 operates to adjust thedistance between the butted planes to be jointed of the two ceramicbodies 401 and 402.

It is possible to obtain the strongest joint in an uniform thicknesswhen the two ceramic bodies 401 and 402 have the butted planes parallelto each other. Even when the joining agent 403 has an uniform thicknessand two ceramic bodies 401 and 402 having the butted planes not parallelto each other, the joining method according to the present inventionmakes it possible to achieve the straight joint in a high accuracy. Inthis case, it is necessary to manage the vertical line to crossrectangularly the terminal planes faced to clamp jigs of the ceramicbodies.

Embodiment 25

FIGS. 49 (A) and (B) are cross sectional view of a holding apparatushaving a clamp angel displacement mechanism formed at the upper clampjig in accordance with the present invention. FIG. 49 (A) shows thestate before the joining process and FIG. 49 (B) shows the state afterthe joining process. In this embodiment, the ceramic body 402 clamped bythe lower clamp jig 405 is fixed to have the axial line coincident withthe vertical line X. The upper clamp jig 404 has a rotator in a sphereform 423 formed at the terminal opposite the clamping side. The rotator423 is supported rotatably with a rotator supporter 424. The rotatorsupporter 424 is placed in a sliding manner in a concave housing 426formed at the terminal of a position adjusting rod 425. The positionadjusting rod 425 makes up a supporter to support movably the rotatorsupporter 424 in a direction crossing the vertical line in a rectangularway. There are arranged spring members 427 and 428 as an actuating meansfor actuating the rotator supporter 424 in a way to locate the rotationcenter (center of the rotator 423) on the vertical line X between theinside wall of the concave housing 426 and the terminal of the rotatorsupporter 424 in a longitudinal direction.

Next, the following description is directed to an operation of thisembodiment. Before the joining process, the upper ceramic body 401 hasthe axial line X1 not coincident with the vertical line X. When thejoining agent melts by the electrical heating, the upper ceramic body401 is released from the lock at the butted plane. The rotator supporter424 supporting movably the upper clamp jig 404 moves at the inside ofthe concave housing 426 in a way to move the rotation center to thevertical line X with the actuating force of the spring members 427 and428. The rotator 423 formed at the upper clamp jig 404 rotates aroundthe rotation center of the rotator supporter 424 in a way to make theaxial line X1 of the clamp jig 404 coincident with the vertical line Xby means of gravity force on the clamp jig 404. As a result, the ceramicbody 402 clamped by the lower clamp jig 405 is joined with the ceramicbody 401 clamped by the upper clamp jig 404 in a manner that the axialline coincident with the axial line of the ceramic body 401 clamped bythe upper clamp jig 404.

It is necessary to form the terminal planes opposite to the buttedplanes of the two ceramic bodies in a way to have each of the axiallines of the two ceramic bodies coincident with that of the clamp jigswhen the two ceramic bodies 401 and 402 are clamped with the clamp jigs404 and 405.

Embodiment 26

This embodiment is an improvement of the Embodiment 25 and is to providea clamp angle displacement mechanism at the fixing side against theclamp jigs at the fixing side in order to join the two ceramic bodies ata joint in a straight line even when the two ceramic bodies have thebutted planes inclined against the axial line and not to cross the axiallines in a rectangular manner. FIGS. 50 (A) to (C) are prepared forexplaining the embodiment. The same elements in FIGS. 50 (A) to (C) asthose of FIG. 49 are provided with the same reference numerals and areomitted in the detailed description. Referring to FIG. 50 (A), a ceramicbody 402' clamped at a lower clamp jig 405 has a terminal plane 402'aopposite to a butted plane inclined against the axial line of theceramic body 402', that is, the terminal plane 402'a and the axial lineof the ceramic body 402' are not in a rectangular crossing. Therefore,the present embodiment is to form a sphere supporter 429 at the terminalplane of the lower clamp jig 405 opposite to the clamping side. Thesphere supporter 429 has a sphere body 430 engaged movably therewith.The sphere body is supported movably by a supporting rod 431. Further,there are provided two vertical line guides 432 and 433 to guide theaxial line of the ceramic body 402' in a vertical direction. As shown inFIG. 50 (B) showing the cross sectional view at B--B line of FIG. 50(A), the vertical line guides 432 and 433 have shapes which are engagedin a sliding manner with the ceramic body 402 at two corners facing toeach other since the ceramic bodies 401 and 402' are in a rectangularcross sectional shape. It is possible to form the vertical line guide ina arbitrary shape in accordance with a cross sectional shape of theceramic body to be jointed.

Even when the terminal plane 402'a of the lower ceramic body 402' isinclined against the vertical line before the joining process as shownin FIG. 50 (A), the sphere supporter 429 rotates around the sphere body430 and the clamp jig 405 is displaced in the angel with the sliding ofthe sphere body 430 on the terminal plane of the supporting rod 431. Asa result, the ceramic body 402' can be supported by the clamp jig 405.At the joining time, the upper clamp jig 404 changes in the angle in asimilar way to that of the FIG. 49. Accordingly, the two ceramic bodies401 and 402' are joined together in a condition that the two ceramicbodies have the axial lines coincident with each other as shown in FIG.50 (C).

Embodiment 27

FIG. 51 (A) and (B) shows an embodiment in which two ceramic bodies arejoined to each other under a horizontal arrangement of two clamp jigs.Especially, the present embodiment is to carry out the joining processwith two ceramic bodies 401 and 402 in a pipe form in a straight joint.A reference numeral 403 denotes a joining agent; a reference numeral 404denotes a clamp jig; and a reference numeral 405 denotes a linkingmember. In FIG. 51 (A), the state before the joining process isexpressed by a broken line and the state after the joining process isexpressed by solid line. The joining agent layer 403 uses a sheet formsubjected to a hole making work. Reference numerals 406 and 407 denote ahorizontal holding guide for holding the two ceramic bodies in ahorizontal direction when the two ceramic bodies 401 and 402 have theaxial lines coincident with each other. The horizontal holding guides406 and 407 have a cross sectional shape shown in FIG. 51 (B).

The linking jig 405 links at the linking plane 405a with the terminalplane of the ceramic body 402 in a pipe form. The linking plane 405a ofthe linking jig 405 is formed to be a rectangular angle against theplane 407a of the horizontal guide member 407 and links with theterminal plane 402a of the ceramic body 402 in a way that the axial lineof the ceramic body 402 can be a horizontal line Y. The terminal plane402a opposite against the butted plane is finished finely to cross theaxial line in a rectangular manner. In order to make up a clamp angledisplacement mechanism for adjusting the angle of the clamp 404, theclamp jig 404 has a sphere supporter 408 formed at the terminal portionopposite against the clamping side thereof. The sphere supporter 408 hasa sphere body 409 included therein. A sphere pressing member 410 islinked with the sphere body 409. The sphere pressing member 410 is madeof a flexible material or is formed into a shape having a flexibleproperty. The sphere pressing member 410 is strained to press, with agiven pressure, the sphere body which displaces in accordance with theinclination. When the joining agent layer 403 melts and solidifies, thesphere pressing member 410 moves in a horizontal direction in order topermit the clamp jig 404 to move in a horizontal direction.

Next, the operation of this embodiment is described. In this embodiment,two ceramic bodies 401 and 402 have the axial lines coincident with eachother by means of a gravity force. When the joining layer 403 is not ina uniform thickness before the joining process, the ceramic body 401having the joining agent layer 403 integrated thereon is arranged in ainclined manner against the axial line of the ceramic body 402 at thefixing side. When the ceramic body 401 is inclined, the sphere supporter408 formed at the terminal portion opposite the clamping side of theclamp jig 404 rotates around the sphere body 409 and the sphere pressingmember 410 having a flexible property is strained. In such a way, theceramic body 401 can be supported. When the joining agent layer melts byheating, the ceramic body 401 is released from the lock at the buttedplane. The rotation function between the sphere supporter 408 and thesphere body 409, the horizontal movement of the clamp jig 404 due to thesphere pressing member 410 and the gravity force make the ceramic body401 has the terminal portion rising upward to be moved downward andthereby the ceramic .body 401 is supported with the horizontal holdingguide 406. As a result, the two ceramic bodies can be jointed to eachother with the axial lines coincident to each other. It is possible toobtain the strongest joint in an uniform thickness when the two ceramicbodies 401 and 402 have the butted planes parallel to each other. Evenwhen the joining agent 403 has an uniform thickness and two ceramicbodies 401 and 402 having the butted planes not parallel to each other,the joining method according to the present invention makes it possibleto achieve the straight joint in a high accuracy.

Embodiment 28

The holding apparatus according to the embodiment 27 requires that theceramic body to be linked with the linking jig 405 must be subjected toa determined fine finishing work. On the other hand, the presentembodiment makes it possible to join the two ceramic bodies even in apoor finishing work and to obtain a straight joint. FIG. 52 shows theoutline of the arrangement of joining method. The same elements in FIG.52 as those of FIG. 51 are provided with the same reference numerals andare omitted in the detailed description. In this embodiment, a clamp jig4105' at a fixing side is provided with a clamp angel displacementmechanism. The clamp angle displacement mechanism at the fixing sidecomprises a sphere supporter 4111, a sphere body 4112 included in thesphere supporter 4111 and a flexible sphere pressing member 4113 linkedwith the sphere body 4112, all of which are formed at the terminalportion of the clamp jig 4111 opposite the clamping side. According tothis apparatus, it is possible to join two ceramic bodies 4101', 4102',4101" and 4102" in a straight line when the ceramic bodies have theterminal portion inclined against the axial lines, that is, the terminalportion do not cross the axial lines at an angle of 90°. In this case itis preferable to select the ceramic bodies having the butted planesparallel to each other if possible.

In the above embodiment, when the joining process is carried out withthe two ceramic bodies having butted planes not parallel to each otherdue to the slightly poor finishing work, the two ceramic bodies areallowably combined at the butted portion to be jointed after the joiningagent melts. As a result, the ceramic bodies show a butted jointslightly curved but are accepted as a product. In the above embodiments24 to 28, the method of A is described but the method of B or C isexecuted with the present method. The method according to the presentinvention can be applicable for the case when one of bodies to bejointed is a metallic body.

The method according to the present invention is provided with a clampangle displacement mechanism and has a feature to displace an angle ofat least one clamp jig in a way to make the axial lines of the twoceramic bodies coincident to each other on melting of the joining agentlayer and to join two ceramic bodies in a straight line even when thejoining agent layer is not uniform thickness or when the joining agentlayer is in a uniform thickness but the two ceramic bodies have thebutted planes not parallel to each other.

The method according to the present invention has an advantage that thetwo ceramic bodies have the axial lines coincident to each other in aneasy and accurate way by using the gravity when two clamp jigs arearranged apart from each other in a vertical direction.

The method according to the present invention provides a clamp angledisplacement mechanism at the fixing side to cause the axial line of theceramic body clamped by a clamp jig at the fixing side to coincide withthe vertical line and accordingly makes it possible to join the twoceramic bodies subjected to a poor finishing work in a straight line.

The method according to the present invention has an advantage that thetwo ceramic bodies have the axial lines coincident to each other in asimple way by using a gravity force when two holding members includingthe clamp jig are arranged independently apart from each other in ahorizontal direction. The method according to the present inventionprovides a clamp angle displacement mechanism for the clamp jig at thefixing side and achieves a joining process in a good condition even whenthe ceramic bodies are subjected to a poor finishing work.

Embodiment 29

(1) First embodiment of 29

FIG. 56 is a structural model view of a joining apparatus according tothe present invention. Reference numerals 501 and 502 denote ceramicbodies in a rectangular bar. It is possible to use the ceramic bodies ina type of either an electric conduction and the non conduction. Numeral503 denotes an solid joining agent in a sheet form or in a paste form,which is inserted between the ceramic bodies to be jointed. The joiningagent has an electric conductivity higher than the two ceramic bodies ata high temperature. During the current supplying, the electric currentflows predominantly through the joining agent. The resultant Juel heatmake joining agent to be melt and react with the ceramic bodies and thusto form a strong joint layer. The joining agent 503 varies in thecomposition with the material variation in the ceramic body. When thejoining agent melts due to the electrical heating, the joining agentgenerates a variation in the composition due to a reaction between theingredients thereof, a reaction with components of the ceramic body anda reaction with the atmosphere and becomes gradually in a higherelectric resistance. Thereby, the current flowing area moves through thebutted planes to be jointed to complete the joining process.Accordingly, the composition of the joining agent layer is differentfrom that of the initial time.

Numerals 504 and 505 are clamp jigs for holding the ceramic bodies 501and 502, respectively in a vertical direction. The upper clamping jig504 is provided firmly with a linking jig or linking membecowork with r507 making up a portion of a control mechanism 506. The linking member507 is composed of a vertical linking portion 507a which moves up anddown along with the vertical axis of the ceramic bodies 501 and 502 anda horizontal linking portion 507b extending in a horizontal direction.It is noted that a holding mechanism for holding movably the linkingmember 507 is omitted. The upper terminal of the vertical linkingportion 507a is joined to a plunger rod 508a of a pressing mechanism 508composed of a liquid cylinder. The liquid supplied to a cylinder room508a is controlled in such a way that the pressing mechanism 508 worksselectively in a way taking either of a pressing state to press theplunger rod 508a or a non-pressing state (P=0) to release the plungerrod 508a to move freely in a vertical axis direction in accordance witha command from the outside. In order to prevent from restricting themovement of the ceramic bodies 501 and 502 in a vertical axis directionby means of the pressing mechanism 508, it is possible not only to setthe pressing mechanism 508 to the non-pressing state (P=0) but also toprevent the plunger rod 508a from being in touch with the verticallinking portion 507a by elevating the plunger rod 508a by a largedistance.

The movement of the horizontal linking portion 507b of the inking member507 is detected by a position sensor 509 such as a differentialtransformer, and the output power of the position sensor is sent to adisplacement detector 510. The position sensor 509 is equipped in a waynot to lock the movement of the horizontal linking portion 507b. Thedisplacement detector 510 transforms a shifting amount of the linkingmember 507 into a signal necessary for a calculation control at acontroller 511. The horizontal linking portion 507b is arranged tocowork with a distance control device 512 for adjusting finally thedistance between butted planes to be jointed of two ceramic bodies 501and 502 by adjusting the position of the horizontal linking portion507b. The distance control device 512 is provided with a rod 512a tovary in the position in accordance with the command from the controller511. The position of the rod 512a determines the lower limit of theposition for the movement of the linking men%her 507. In this apparatus,the linking member 507 and the distance control device 512 build up adistance control mechanism.

A reference numeral 513 is an electric source for supplying an electriccurrent through a electrode 514 to the joining agent 503 and portion ofthe ceramic bodies at the vicinity of the joining agent in accordancewith the command from controller 511. A reference numeral 515 is a torchto inject a flame for pre-heating the butted portion to be jointed. Thenumber and the installing position of the electrode and the torch can bedetermined arbitrarily. It is possible to install the electrode 514 within the torch 515. Such a construction make handling of sample easy andapparatus size compact. Electrode may be a rod or plate shape. Whilecurrent supplying may be executed by discharge in air between theelectrode and the butted portion to be jointed which are apart from eachother, close positioning of the electrode and the butted portion permitcurrent supplying without generation of discharge in air to result indepression of equipment cost due to decrease in required power,improvement of safety and decrease in partially decomposition anddeterioration of the butted portion due to over-heating. In thisembodiment, two electrodes 514, 514 are positioned in a way to face toeach other against the butted portion to be jointed and two torches 515,515 are also positioned in a similar way to face to each other. Arelative movement of the butted portion can be achieved by moving theceramic bodies 501 and 502 without moving the electrodes 514 and thetorches 515 or by moving the electrodes 514 and the torches 515 withoutmoving the ceramic bodies 501 and 502. On contrary to the relativemovement, the joining process may be carried out by contacting aplate-like electrode to the whole length to be jointed, or by supplyingcurrent to a plurality of electrodes arranged along the portion to bejointed, or by supplying current between a pair of selected electrodesarranged around the portion to be jointed by switching.

Next, the description is directed to a method for joining two ceramicbodies by using an apparatus according to the embodiment shown in FIG.56. There may be various ways for the operation modes of the pressingmechanism 508 and the distance control device 512. The pressingmechanism 508 and the distance control device 512 are controlled in away shown in a position shifting curve of FIG. 57. The position shiftingcurve of FIG. 57 is obtained from the output signal of the positiondetector 510 which has the output signal set to 0 when the pre-heatingstarts. At a time t1, the pressing mechanism 508 is set to a releasestate (P=0) so as to release the two ceramic bodies from the fixing tothe pressing mechanism 508. Then, the portion to be jointed are ispreheated by the flame injected from the torch 515 until the temperatureat the portion to be jointed reaches about 800° C. The pre-heating timeis expressed by a time period from t1 to t2. Since the pressingmechanism 8 is in a release state during this time period, the twoceramic bodies to be jointed 501 and 502, the clamp jig 504, and thelinking member 507 are released from being locked with the outside.Therefore, the two ceramic bodies 501 and 502, the joining agent, theclamp jig 504, and the linking member 507 are in a position to executefreely the thermal expansion. Accordingly, the position detector 510 hasthe output signal varying in a expansion direction with the time passageof t1 to t2. At the pre-heating stage, the joining agent does not melt.When the output signal of the position detector 510 indicates thesaturation of expansion, the controller 511 sends to the distancecontrol device 512 a command signal and then the distance controller 512manages the rod 512a to move to a given position. After completion ofthe pre-heating, the portion to be jointed is energized and is heated upto a higher temperature so that the joining agent melts and shrinks. Onthe other hand, the two ceramic bodies 501 and 502, the clamp jigs 504and 505 and the linking member 507 continue still the expansion. Thewidth between the butted planes to be jointed decreases regardless ofthe heat expansion, which cause the two ceramic bodies 501 and 502, theclamp jigs 504 and 505 and the linking member 507 to expand until thehorizontal linking portion 507b of the linking member 507 links to therod 512a. When the horizontal linking portion 507b links to te rod 512a,the portion over the horizontal linking portion 507b of the verticallinking portion 507a extends upward due to the thermal expansion and theportion below the horizontal linking portion 507b of the verticallinking portion 507a extends downward. That is, the clamp jig 504 andthe ceramic body 501 extend downward and the ceramic body 502 and theclamp jig 505 extend upward. Therefore, it is necessary to take theexpansion into consideration for determination of the distance betweenthe two ceramic bodies, which is set to the distance control device 512.Otherwise, the actual distance between the butted planes is smaller thanthe set distance. This may cause the defective joint. It is preferableto carry out the control due to the controller 511 under considerationof the expansion on current supplying. The controller 511 of presentembodiment calculates the distance between the butted planes of the twoceramic bodies necessary for the formation of the suitable joint byconsidering the temperature distribution obtained from the thermalconduction analysis and the thermal expansion coefficient and determinesthe position of the rod 512a by driving the position control device 12in order to hold a distance L1 for the ceramic body 501 to move down ina purpose to hold the calculated distance. In an alternative way, it ispossible to obtain the distance through the preliminary experiment andto command the controller 511 to memorize the data L1 from thepreliminary experiment. By the way, the preferable distance between thebutted planes of the two ceramic bodies is in a range from 100 to 400micron, which varies with the joining agent and the quality of ceramicbody.

At a time t2, the controller 511 commands the electric current supplyingsource 513 to manage an electric current in a given size to flow intothe electrode 514 for starting the current supplying to the portion tobe jointed. At a time passing through a period after the initiation ofthe current supplying, the joining agent 503 starts to melt and theceramic body 501 moves downward with the sum weight of the ceramic body501 itself, the clamp jig 504 and the linking member 507. After theceramic body 501 moves downward to a position at which the horizontallinking portion 507b links to the rod 512a of the distance controldevice 512, the two ceramic bodies 501 and 502 extend due to the thermalexpansion with the heat generated by the electric current from theelectrode 514 so as to decrease the distance between the butted planes.As mentioned above, the controller 511 sets the distance L1 underconsideration of the expansion after the current supplying. Therefore,it is possible to maintain the distance between the butted planes of twoceramic bodies within a range (100 to 400 micron) necessary forobtaining the superior joint, even if large expansion may generate aftercurrent supplying. The current supplying through the electrode iscontinuing at a time t3. During this period, the joining agent 503sufficiently melts and reacts with the two ceramic bodies 501 and 502.

At a time (t3) when the joining agent 503 reacts completely with the twoceramic bodies 501 and 502, the controller 511 commands the distancecontrol device 512 to move the rod 512a downward and at the same time,commands the pressing mechanism 508 to enter into the pressing state. Asa result, at a time t3, the two ceramic bodies 501 and 502 are pressedin a direction to be jointed and the molten joining agent in a largeportion of the total amount is pushed away from the butted planes to bejointed of the two ceramic bodies. At the same time, the two ceramicbodies complete the joint. The current supplying to the portion to bejointed is terminated just before or after the operation of the pressingmechanism 508 or at the same time of operation of the pressing mechanism508. In such a way, the two ceramic bodies to be jointed are broughtinto a close contact to each other through a thin joining layer and arejoined to each other at a high strength upon being cooled.

Two silicon nitride ceramic bodies in a size of 15×15×200 mm are joinedby using a joining agent including, as an electric conductive component,calcium fluoride with the joining method mentioned above. The electricvoltage is applied across the two electrodes 514 so that the electriccurrent of 0.8 A flows across the two electrodes 514. The preheatingtemperature is 800° C. (10 min), and the time period between t2 and t3is about 6 min. The pressing pressure of the pressing mechanism 508 is100 g/mm². It is confirmed that the average value of the joint strengthis about 300 MPa at a room temperature after a four point bending testwith ten samples. It should be noted that a very weak joint strength tocrack at the joint during the working of test samples is given to thejoint obtained with same joining condition such as current supplyingcondition and the pre-heating temperature except for the additionaloperation that the two ceramic bodies are pressed at a given pressure bythe pressing mechanism 508 at the pre-heating stage.

In the above embodiment, the rod 512a of the distance control device 512is moved down after the preheating. However, in case of a high thermalexpansion, it is allowable to elevate the rod 512a in order to set thedistance between the butted planes of the two ceramic bodies to asuitable size.

In the above embodiment, the distance between the butted planes of thetwo ceramic bodies are adjusted in such a way that the two ceramicbodies move down to a given position by the action of the gravity afterthe initiation of the current supplying at a time t3. As an alternativeway, it is possible to achieve the aimed distance (L_(o) →L_(o3)) bymoving step by step the rod 512a of the distance control device 512after the initiation of the current supplying at a time t2 as shown inthe position shifting curve of FIG. 58. Further the aimed distance canbe achieved by a continuous movement of the rod 512a not by the gradedmovement of the rod 512a. When the distance between the butted planes ischanged in a graded way or in a continuous way, it is possible to changethe distance between the butted planes in accordance with the variationin melting condition of the joining agent due to the current supplying.As a result, the distance between the butted planes of the two ceramicbodies can be made set to almost the most suitable value in accordancewith the decrease in the voluble of the joining agent due to the meltingwithout pushing out the molten joining agent in an amount larger thanthe necessary amount.

Further, it is possible to control the distance control device 512 bymanaging the controller 511 to receive, as a controlling variable, oneof the data of the voltage, electric current, electric power sent to theelectrode, the joining temperature and the shifting amount of theceramic body.

Embodiment 29-2

FIG. 59 is an outline drawing of a joining apparatus for joining ceramicbodies placed in a horizontal position. In FIG. 59, the functions thesame as those of FIG. 56 are provided with the reference numerals thesame as those of FIG. 56 and are omitted in the detailed description. InFIG. 59, two ceramic bodies 501 and 502 are in a pipe form and a joiningagent 503 is formed into a ring form. An electrode 514 is positioned ina torch 515 for injecting a flame. The electrode 514 and the torch 515rotate around the portion to be jointed. Any other method than the abovemethod to heat the whole of the butted portion to be jointed isapplicable.

One is a method of rotating the body to be jointed under fixing theelectrode. The other is a method that under fixing the body to bejointed and the electrode, the current is supplied between the twoselected from a plurality of electrodes arranged around the periphery ofthe body to be jointed by means of switching in a way that the suppliedarea moves from one to another in turn.

In this embodiment, the two ceramic bodies are placed in a horizontalposition and are joined to each other. The joining apparatus accordingto this embodiment has a supporting body 516 for supporting the clampjig 505 and a ceramic supporting bodies 517 for supporting the twoceramic bodies 501 and 502. The ceramic body 101 does not move with thegravity in a different way from that of FIG. 56. A rod 512a of adistance control device 512 is linked to a linking portion 507b. Inorder to prevent each thermal expansion of members of the joiningapparatus from being locked, the distance control device 512 is in astructure not to lock the free movement of a linking member 507 in anon-operation state in a similar way to that of the liquid cylinder ofthe pressing mechanism 508. It is necessary to operate immediately thedistance control device 512 after saturation of the thermal expansion inorder to carry out the position shift shown in FIGS. 57 and 58. When thetwo ceramic bodies to be jointed are pressed by a pressing mechanism508, the distance control device 512 is required to be again in anon-operation state, and the pressing must be carried out by thepressing mechanism 508. The control of these members are executed by thecommand of the controller 511.

A joining process is carried out with the joining apparatus of thisembodiment under a position shifting curve the same as that of FIG. 57.The two ceramic bodies 501 and 502 are silicon nitride ceramic bodies ina 18 mm outside diameter, 6 mm inner diameter and 200 mm long. Theelectrode 514 rotates at a rate of 100 rpm. The pre-heating temperatureis about 800° C. The electric voltage is applied across the twoelectrode 514 so that the electric current of 0.6 A flows across the twoelectrodes 514 and the time period between t2 and t3 is about 5 min. Thepressing pressure of the pressing mechanism 508 is 100 g/mm². The timingfor the termination of the current supplying is carried out in a similarway to that of FIG. 56. The gas tight test is carried out with 10 piecesof samples and indicates no sample having the gas leakage. It isconfirmed that the average value of the joint strength is about 270 MPaat a room temperature after a four point bending test.

Embodiment 29-3

FIG. 60 is an outline drawing of another joining apparatus forpracticing the joining method according to the present invention. InFIG. 60, the functions the same as those of FIGS. 56 and 59 are providedwith the reference numerals the same as those of FIGS. 56 and 59 and areomitted in the detailed description. A difference point between theapparatus of FIG. 60 and those of FIGS. 56 and 59 is that the saturationof the thermal expansion and the distance between the butted planes ofthe two ceramic bodies are observed directly with a enlarging inspector509 having a television camera and an enlargement lens equipped thereonand the control is carried out by the observation data. The distancebetween the butted planes of the two ceramic bodies are measured withthe enlarging inspector 509. On the basis of the observation date, thecontroller 511 manages the distance control device 512 to drive the rod512a in a way to obtain the most suitable value of the distance betweenthe butted planes. The driving pattern of the rod 512a is arbitrary. Thedistance control device is in a structure not to lock the movement ofthe linking member 507 at the non-operation state in a similar way tothat of the distance control device of FIG. 59. According to thisapparatus to observe directly the distance between the butted planes, itis not necessary to obtain the shifting amount of the ceramic bodies 501by carrying out a preliminary experiment or by carrying out acomplicated calculation. Further, this apparatus has another advantagethat the distance between the butted planes is adjusted in the mostsuitable way since the direct measurement data on the distance with theenlarging inspector 5112 is feedbacked to the controller 511.

In the embodiments shown in FIGS. 56 and 60, since the two ceramicbodies are in a rectangular bar form, a relative movement between theceramic bodies to be jointed and the electrode are carried out. When theceramic body is in a round bar form or a round pipe form, the ceramicbodies can be rotated by placing on a supporting block rotating andjoined with a motor positioned beneath the clamp jig 502 with fixedatate of the electrode in a similar way to that described in theJapanese Patent Publication (examined) 1988-225583.

The joining apparatus shown in FIGS. 56 and 59 use, as a position sensor509, the position sensor in a contact type but can use the positionsensor in a non-contact type such as magnetic or optical method. Themeasuring point of the position sensor 509 and the operation point ofthe distance control device are placed on the linking member 507 in thesame way as each other but can be placed at the different positions fromeach other.

In a process to practice the joining method according to the presentinvention, the control mode after the saturation of the thermalexpansion is arbitrary. The joining can be performed with a positionshifting curve other than those of FIGS. 57 and 58. For example, whenthe ceramic body is relatively light, the ceramic body 501 can be moveddown only by the gravity without in the apparatus of FIGS. 56 and 60using distance control mechanism after the saturation of the thermalexpansion. Then it is possible to press the ceramic bodies with thepressing mechanism after the termination of the shifting of the distancebetween the butted planes of the two ceramic bodies 501 and 502. Whenthe ceramic body 501 is heavy, it is possible to control only with theposition control mechanism without using the pressing mechanism.

The saturation of thermal expansion is performed only by the pre-heatingin the above embodiment but can be performed by the pre-heating and thecurrent supplying when the current supplying is executed before thesaturation.

The pre-heating is carried out by using the torch such as a gas burnerin the embodiment but can be performed by using other heating method.

The joining method according to the present invention manages a controlmechanism not to prevent the two ceramic bodies from moving freely in anaxial direction. When the joining agent, ceramic bodies, and jigsperform the thermal expansion, the clamp jig and the structural portionof the control mechanism are free from the strain because the thermalexpansion is not suppressed by the jig system. This is an advantage notto damage the jig system and to solve the problem to make the distancecontrol uncertain when the distance control mechanism is used. As aresult, a atable current supplying is can be performed without pushingout extremely the melt joining agent between the planes to be jointedduring the current supplying and thus a good joined body is obtained

Further, the joining method according to the present invention has anadvantage to perform the more accurate control by making the effect ofthe thermal expansion as low as possible because the control mechanismis operated after the measurement and completion of saturation of thethermal expansion.

Embodiment 30

FIG. 61 is a structural model view of a joining apparatus according tothe present invention. Reference numerals 601 and 602 denote ceramicbodies in a pipe form. It is possible to use the ceramic bodies in atype of either an electric conduction or the non conduction. Numeral 603denotes an solid joining agent in a ring sheet form. The joining agent603 varies in the composition with the variation in the ceramic bodymaterial and is described in detail in the Japanese Patent Publication(examined) 1987-65986 and other Japanese Patent publications. Therefore,the detailed description with the joining agent is omitted. Numerals 604and 605 are clamp jigs for holding the ceramic bodies 601 and 602,respectively in a vertical direction. The upper clamping jig 604 isprovided in a fixed manner with a linking jig or linking member 607making up a portion of a control mechanism 606. The linking member 607is composed of a vertical linking portion 607a which moves up and downalong with the vertical axis of the ceramic bodies 601 and 602 and ahorizontal linking portion 607b extending in a horizontal direction. Itis noted that a holding mechanism for holding movably the linking member607 is omitted. The upper terminal of the vertical linking portion 607ais joined to a plunger rod 608a of a pressing mechanism 608 composed ofa liquid cylinder. The liquid supplied to a cylinder room 608b iscontrolled in such a way that the pressing mechanism 608 worksselectively in a way taking either of a pressing state to press theplunger rod 608a or a non-pressing state (P=0) to release the plungerrod 608a to move freely in a vertical axis direction in accordance witha command from the outside. In order to prevent the pressing mechanism608 from restricting the movement of the ceramic bodies 601 and 602 in avertical axis direction, it is possible not only to set the pressingmechanism 608 to the non-pressing state (P=0) but also to prevent theplunger rod 608a from being in touch with the vertical linking portion607a by elevating the plunger rod 608a by a large distance.

The movement of the horizontal linking portion 607b of the linkingmember 607 is detected by a position sensor 609 such as a differentialtransformer, and the output power of the position sensor is sent to adisplacement detector 610. The position sensor 609 is equipped in a waynot to lock the movement of the horizontal linking portion 607b. Thedisplacement detector 610 transforms a displacement amount of thelinking member 607 into a signal necessary for a calculation control ata controller 611.

The horizontal linking portion 607b links with a load balance device 612for balancing apart of the sum W1 of the weight of the ceramic body 601placed at the upper position and the weight of the clamp jig 604 and thelinking portion 607 (external load) with a balance load W2 andtransforming the weight of the ceramic body and the external load into asmall apparent load. The load balance device 612 transmits the force tothe horizontal linking portion 607b through a rod 612a. The load balancedevice 612 is to generate a balance load to be subtracted from the sumof the weight of the upper ceramic body and the external load and iscomposed of a liquid cylinder in this embodiment. The supportingstructure of the linking member 607 (not shown) is constructed in such away that when the rod 612a of the load balance device 612 is actuated tomove upward, the linking member 607 also receives a force acting upward.It is possible to supply the vertical linking portion 607a with a forceacting upward by linking the rod 612a with the horizontal linkingportion 607b through a supporting point prepared at the medium point ofthe horizontal linking portion 607b and by actuating the rod 612a tomove downward. The balance load W2 generated from the load balancedevice 612 is set to a value smaller than the sum W1 of the weight ofthe ceramic body and the external load against the ceramic body 601placed at the upper position and the jig system (604, 607). Accordingly,the apparent weight Wo of the ceramic body placed at the upper positionis W1-W2. The apparent weight Wo differs with the joint area and isseveral g per unit area.

A reference numeral 613 is an electric source for supplying an electriccurrent through a electrode 614 to the butted portion composed of thejoining agent 603 and the ceramic bodies at the vicinity of the joiningagent in accordance with the command from controller 611. A referencenumeral 615 is a torch to inject a flame for pre-heating the buttedportion. The number and the installing position of the electrode and thetorch can be determined in a arbitrary way. It is possible to installthe electrode 614 with in the torch 615. In this embodiment, twoelectrodes 614, 614 are positioned in a way to face to each otheragainst the portion to be jointed and two torches 615, 615 are alsopositioned in a similar way to face to each other. A relative movementbetween the two ceramic bodies 601 and 602 and the electrode 614 and thetorch 615 can be generated along the portion to be jointed by rotatingthe electrode 614 and torch 615 around the portion to be jointed.

Next, the description is directed to a method for joining two ceramicbodies by using an apparatus according to the embodiment shown in FIG.61. A curve of FIG. 62 is a displacement curve showing the movement ofthe horizontal linking portion 607b (displacement at the joint layer)and is obtained from the output signal of the displacement detector 610which has the output signal set to 0 when the pre-heating starts. At atime t1, the pressing mechanism 608 is set by the controller 611 to arelease state (P=0) so as to release the two ceramic bodies 601 and 602from the fixing in an axial direction. The controller 611 con, hands theload balance device 612 in order to decrease the sum of the ceramic bodyplaced at the upper position and the clamp jig 604 and the linkingmember 607. The load balance device 612 provides the horizontal linkingportion 607b with the balance force in accordance with the command fromthe controller 611 and decreases the apparent weight of the ceramic bodyplaced at the upper position. Then, the portion to be jointed arepre-heated by the flame injected from the torch 615 until thetemperature at the butted portion reaches about 800° C. The pre-heatingtime is expressed by a time period from t1 to t2. Since the pressingmechanism 608 is in a release state during this time period, the twoceramic bodies 601 and 602, the clamp jig 604, and the linking member607 are released from being locked with the outside. Therefore, the twoceramic bodies 601 and 602, the joining agent 603, the clamp jig 604,and the linking member 607 are in a position to execute freely thethermal expansion. Accordingly, the displacement detector 610 has theoutput signal varying in a expansion direction with the time passage oft1 to t2. At the pre-heating stage, the joining agent does not melt. Atthe same time the displacement detector 610 detects the saturation ofthe thermal expansion or at t2 after a time passed, the controller 611sends to the current supplying source 613 a command to supply electriccurrent to the butted portion. After pre-heating, the portion to besupplied current is heated up to a higher temperature and the joiningagent melts and shrinks. On the other hand, the two ceramic bodies 601and 602, the clamp jig 604 and 605, and the linking member 607 continuestill the expansion. Even with the continuation of the expansion of theceramic body 601 and so on, the load balance device 612 is onlybalancing the load. Hence, the ceramic body placed at the upper positionis in the apparent weight Wo and moves down gradually. Finally themovement stops, and the displacement reaches the saturation. During thistime, the joining agent 603 melts completely and reacts with the twoceramic bodies sufficiently.

The displacement detector 610 detects the saturation of the displacementamount of the ceramic body 601 and at the same time or at a time t₃after a given time has passed, the controller 611 commands the pressingmechanism 608 to press the ceramic body placed at the upper positionagainst the ceramic body placed at the lower position. As a result, at atime t3, the two ceramic bodies 601 and 602 are pressed in a joineddirection. At the same time, the two ceramic bodies complete thejoining. The current supplying of the portion to be jointed isterminated just before or after the operation of the pressing mechanism608 or at the same time of operation of the pressing mechanism 608. Insuch a way, the two ceramic bodies are brought into a close contact toeach other through a thin joining layer and are joined to each other ata high strength upon being cooled.

Two silicon nitride ceramic bodies in a pipe form of an outside diameter60 mm, an inner diameter 45 mm and a length 100 mm are joined by using ajoining agent including, as an electric conductive component, calciumfluoride. The joining agent 603 is applied in an initial thickness of400 micron. As the sum W1 of the weight of the coated ceramic body 601placed at the upper position and the external load 1877 g, the loadbalance W2 caused by the load balance device 612 is set to 1847 g.Accordingly, the apparent weight Wo becomes 30 g. The pre-heatingtemperature is 800° C. (15 min). The electric current is graduallyincreased and kept at 0.8 A. The time period between t2 and t3 is about10 min. The current supplying is stopped at a time t₃. The pressingpressure of the pressing mechanism 608 is set to 5 Kg/mm². At a time t3,the joint layer comes to here a thinner thickness, for example 20 micronin a thickness. A gas tight test with a helium detector indicates thatthere is no sample showing the gas leak among 10 test pieces. It isconfirmed that the average value of the joint strength is about 300 MPaat a room temperature after a four point bending test with a sample inJIS size.

For a comparison, two ceramic bodies are joined with the same conditionas that of the above embodiment except for no use of a load balancedevice 612. At this time, the shifting curve is in a pattern shown by acurve b of FIG. 62. As shown in a curve b of FIG. 62, when the joiningagent starts melting upon initiation of the electric current supplying,the ceramic body placing at the upper position starts rapidly movingdown. Then the displacement amount reaches the saturation value at theearly stage. When the resultant joint is tried to be cut to a size ofthe JIS testing sample, the joint is cracked. Then, it is impossible tocarry out the bending test for measuring the joint strength. The reasonis that the molten joining agent is extruded from the planes to bejointed before the sufficient reaction with the two ceramic bodies.

In the above embodiment, the pressing mechanism 608 executes thepressing operation after the saturation of the displacement amount uponthe initiation of electric current supplying. However, it is possible tocarry out the pressing operation with the pressing mechanism 608 beforethe saturation of the displacement amount under a condition after themolten joining agent reacts sufficiently with the two ceramic bodies.The saturation displacement amount means the completion of a sufficientreaction between the joining agent and the two ceramic bodies, whichresults in the thin joint layer and the resultant sample ensures a jointstrength sufficiently high upon cooled after termination of the currentsupplying.

In the above embodiment, which the load balance device 612 is composedof a liquid cylinder, it is possible to use any type of mechanismcapable of balancing the load such as a power increasing mechanism basedon a lever principle or a pulley principle.

The method according to the present invention can decrease the apparentweight of the ceramic body placed at the upper position by balancing theweight of the ceramic body and the external load with the balance loadeven when the ceramic body placed at the upper position and the externalload is heavy. Therefore, in a joining method to move downward theceramic body placed at the upper position by the gravity action, it ispossible to move downward the ceramic body placed at the upper positionin accordance with the shrinkage of the molten joining agent underexecuting the reaction between the molten joining agent and the twoceramic bodies only by changing the balance load in accordance with theweight of the ceramic body placed at the upper position.

A method according to the present invention is to press the ceramic bodyplaced at the upper position against the ceramic body placed at thelower position at the final joining step. Therefore, this method iscapable of forming the joint layer in a high density by expelling thegas included in the joint layer and of correcting the inclined planebetween the two ceramic bodies at the upper and lower positions.

The method according to the present invention is to prevent theexcessive electric current supplying by terminating the currentsupplying upon detection of the saturation of the displacement amount.

Embodiment 31

FIG. 63 is a side view of a T-joint manufactured by the electric joiningmethod according to the present invention. FIG. 64 is a cross sectionalview obtained by cutting at II--II line of FIG. 63. FIG. 65 is anenlargement of a portion shown by a circle in FIG. 64. The T-joint of aceramic pipe is used not only for a joint but also for a housing ofvalve. A reference numeral 701 denoted a first ceramic pipe for makingup a main path member subjected to a planer work at the outsideperiphery and a reference numeral 702 denotes a second ceramic pipe formaking up a blanch path member connected to the first ceramic pipe. Itis noted that the ceramic pipe is composed of a silicon nitride ceramicor syalon.

The first ceramic pipe 701 has a flat plane 703 for forming a buttedplane at the outside periphery thereof. In a case of formation of theflat plane 703, a ceramic pipe is provided with a reference workingplane 704. The reference working plane 704 is prepared for preventingthe ceramic pipe 701 from rolling. The flat plane 703 can be formed byshaving the outside periphery with a NC working machine under fixing theceramic pipe 701 at the reference working plane 704 on a working desk.The both terminals of the flat plane 703 in an axial direction havetapers 705 for causing a joining torch T to enter easily. Next, the flatplane 703 has a through hole formed therethrough by a drill. The throughhole 706 is composed of a hole having a small diameter 706a and a hole706b having a large diameter. The large hole 706b and a ring flat plane706c make up a stair engagement. A corner 706b1 positioned at theopening of the large hole 706b is tapered. A corner 706b2 between theanother terminal of the large hole 706b and the ring flat plane is madecurved.

Next, the second pipe is described. A ceramic pipe is shaved at oneterminal in a axial line through all periphery and has a convex cylinder707 and a butted plane 708 formed thereon. The size l in a radiusdirection is set to a relatively larger value in order to achieve asufficiently high strength at the joint portion when the ceramic pipesare joined electrically. For example, it is preferable to make the sizel more than 4 mm with a second ceramic pipe of an outside diameter 30 mmand an inside diameter 16 mm. The terminal 707a at the outside of theradius direction of the convex portion 707 is tapered at a given angleand the corner 707b at the base portion is curved. In such a way, theformation of the taper (706b1, 707a) and the curve (706b2, 707b)releases the generation of the concentration of stress at the cornerduring the solidification of the joining agent at a joining step andprevents the ceramic pipe from cracking. The taper and the curve arealso useful for preventing the ceramic pipe from cracking during thehandling and the heating.

A gap g is formed between the ring flat plane 706c and the terminalplane at the convex portion 707 under the engagement between the largehole 706b and the convex portion 707 constructing the stair engagement.When the joining agent melts and shrinks in the volume, the gap g is toexecute a function to prevent the generation of poor joints bydecreasing the distance between the butted planes of the two ceramicpipes in accordance with the melting and the volume shrinkage of thejoining agent. The size tolerance of the large hole 707b and the convexportion 707 must be made a value to permit both to move smoothly evenwhen the ceramic pipes 701 and 702 generate the difference in thethermal expansion due to the temperature difference. As a practicalmatter, the clearance after the thermal expansion is set to a value of agap caulking (H7 and f6 relation) in a common use.

In order to suppress the degradation of the joining strength obtainedwith an electric joining method, it is preferable that the flat plane703 and the butted plane 708 have a surface roughness less than 10 S.This embodiment uses about 2 S.

Next, the following description is directed to a working step underinserting the joining agent between the flat plane 703 and the buttedplane 708.

The electric joining can be carried out by the joining method type A,which comprises following steps of inserting a joining agent between thelarge flat plane 703 of a first ceramic pipe 701 and the butted plane708 to be jointed of the second ceramic pipe, pre-heating the buttedportion with the flame from the joining torch T approaching closethereto, heating the joining agent with the Joule heat caused bysupplying current to a high temperature for short time to melt thejoining agent and then joining strongly the ceramic bodies.

When a ceramic pipe in a long size, a plurality of short ceramic pipes709 are combined to each other as shown in FIG. 66. The gap g is formednecessarily when plurality of ceramic pipes are combined to each other.

In the above embodiment, the joining process is carried out by anelectric joining method type A but the other types are applicable.Further it is possible to use a conventional furnace heating method toheat the joining agent in a furnace and carry out the joining process.

The ceramic joint which can be manufactured by the method according tothe present invention is not limited to the T-joint in the aboveembodiment. Y-joint, a cross joint or any other ceramic joint can bemanufactured by the method according to the present invention.

As explained clearly above, the joining method according to the presentinvention is to form a flat plane on the outside periphery of a firstceramic pipe with a planer working and can join the first ceramic pipeand the second ceramic pipe at the flat portion to enable thecomplicated joint manufacturing at a low cost and a short time. Furtherit is possible to reduce the size error in the distance between thebutted planes to be jointed and to obtain the sufficiently high joiningstrength according to the joining method according to the presentinvention.

The joining method according to the present invention comprises thesteps of forming a stair engagement portion at the terminal of the flatplane side of the through hole and forming engagement convex portionwhich is engaged with the stair engagement at the terminal where thebutted plane of the second ceramic pipe is formed. Accordingly, thismethod makes it easy to determine the position of the two ceramic pipeswhen the joining agent is inserted between the two ceramic pipes. Thestair engagement and the engagement convex portion are formed in a waythat the gap is formed between the stair engagement and the engagementconvex portion under a state to engage the stair engagement with theengagement convex portion. Therefore, when the joining agent shrinksupon solidification thereof, it is possible to decrease the distancebetween the butted planes of the two ceramic pipes in accordance withthe shrinkage. As a result, there is no generation of poor joint.

A formation of a large flat plane makes it possible to arrange thejoining torch at the most suitable position and to ensure the good jointwith the electric joining method.

Joining Agent For Use in Silicon Nitride Ceramic

In the following embodiments, a joining agent is a mixture of variouspowders in a given mixing ratio and is of a paste form incorporated withorganic binder solved in a solvent such as acetone or toluene.

A test piece for strength test (bending test) is prepared by makingjointed silicon nitride ceramic body obtained by joining two siliconnitride square bars in a size of 15 mm×15 mm×20 mm with the joiningagent. A ceramic square bar in a size of 3 mm×4 mm×40 mm (JIS size) isobtained by cutting the jointed ceramic bodies. The used joining agentis in an amount of 50 mg/cm². The strength test is carried out with thetest piece in a JIS form at the following condition by using a fourpoints bending test: An upper span is 10 mm, and a lower span is 30 mm.The loading rate is 0.5 mm/min. The testing result is shown by theaverage value Mpa (mega pascal) obtained with 10 testing piecessubjected to the four points bending test.

The electric joining method is carried out at the following condition:The pre-heating is carried out up to a temperature of 800° to 900° C.with a mixing gas of propane and oxygen. The flowing electric currentthrough the joining agent is 0.6 to 1 A. The electrode is moved at arate of 5 cm/min to heat all of the joining agent. In the followingembodiment, the table showing experimental data is described in acollection manner after description of the invention.

Embodiment 32

In order to confirm the effect of the joining agent shown by claim 25,the joining agent in a composition of CaF₂ and Al₂ O₃ in a mixing ratioshown in Table 1 is tested with the joint strength at room temperatureand at 1000° C. The joining agent including 10 to 40 weight % of Caf₂,60 to 90 weight % of Al₂ O₃ (range attached with a symbol *) shows thestrength higher than 210 MPa at a temperature range of room temperatureto 1000° C.

The joining agent in a composition of CaF₂, Al₂ O₃ and SiO₂ in a mixingratio shown in Table 2 is tested with the joint strength at roomtemperature and at 1000° C. The joining agent including 10 to 40 weight% of Caf₂, more than 10 weight % of Al₂ O₃ and more than 10 weight % ofSiO₂ shows the strength higher than 250 MPa at a temperature range ofroom temperature to 1000° C.

Embodiment 33

In order to confirm the effect of the joining agent of claim 26, thejoining agent in a composition of CaF₂, Al₂ O₃ and Y₂ O₃ in a mixingratio shown in Table 3 is tested with the joint strength at roomtemperature and at 1000° C. The joining agent including 10 to 40 weight% of Caf₂, more than 10 weight % of Al₂ O₃ and 10 to 55 weight % of Y₂O₃ shows the strength higher than 300 MPa at a temperature range of roomtemperature to 1000° C.

The joining agent in a composition of CaF₂, Al₂ O₃, SiO₂ and Y₂ O₃ in amixing ratio shown in Table 4-1 to 4-3 is tested with the joint strengthat room temperature and at 1000° C. The joining agent including 10 to 40weight % of Caf₂, more than 10 weight % of Al₂ O₃, 10 weight % SiO₂ and10 to 55 weight % of Y₂ O₃ shows the strength higher than 350 MPa at atemperature range of room temperature to 1000° C.

Embodiment 34

In order to confirm the effect of the joining of claim 27, the joiningagent in a composition of CaF₂, Al₂ O₃, and Si₃ N₄ in a mixing ratioshown in Table 5 is tested with the joint strength at room temperatureand at 1000° C. The joining agent including 10 to 40 weight % of CaF₂,15 to 45 weight % of Si₃ N₄ and the residual of Al₂ O₃ shows thestrength higher than 300 MPa at a temperature range of room temperatureto 1000° C.

The joining agent in a composition of CaF₂, Al₂ O₃, SiO₂ and Si₃ N₄ in amixing ratio shown in Table 6-1 to 6-3 is tested with the joint strengthat room temperature and at 1000° C. The joining agent including 10 to 40weight % of CaF₂, more than 10 weight % of Al₂ O₃, more than 10 weight %of SiO₂ and 15 to 45 weight % of Si₃ N₄ shows the strength higher than350 MPa at a temperature range of room temperature to 1000° C.

Embodiment 35

In order to confirm the effect of the joining agent of claim 28, thejoining agent in a composition of 30 weight % of CaF₂, 20 weight % ofAl₂ O₃, 25 weight % of Y₂ O₃ and 25 weight % of Si₃ N₄ is tested withthe joint strength at room temperature and at 1000° C. The strength atroom temperature is 425 MPa and the strength at 1000° C. is 422 MPa.

The joining agent in a composition of 30 weight % of CaF₂, 15 weight %of Al₂ O₃, 15 weight % of SiO₂, 20 weight % of Y₂ O₃ and 20 weight % ofSi₃ N₄ is tested with the joint strength at room temperature and at1000° C. The strength at room temperature is 465 MPa and the strength at1000° C. is as high as 470 MPa.

                  TABLE 1                                                         ______________________________________                                        Samples   CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                        Room Temp                                                                              1000° C.                           ______________________________________                                        *1         0     100       --       --                                         2         5     95         92      101                                       *3        10     90        230      228                                       *4        20     80        259      262                                       *5        30     70        283      288                                       *6        40     60        265      212                                        7        45     55        259      137                                        8        50     50        244       71                                       ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Samples                                                                              CaF.sub.2                                                                              Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          Room Temp  1000° C.                       ______________________________________                                        1       5       10      85    35         54                                   2       5       50      45    61         55                                   3       5       85      10    27         19                                   4      10        5      85   251        213                                   *5     10       10      80   262        258                                   *6     10       45      45   266        271                                   *7     10       80      10   259        258                                   8      10       85       5   208        214                                   9      30        5      65   289        230                                   *10    30       10      60   305        275                                   *11    30       35      35   319        333                                   *12    30       60      10   298        296                                   13     30       65       5   238        244                                   14     40        5      55   263        203                                   *15    40       10      50   267        255                                   *16    40       30      30   289        293                                   *17    40       50      10   301        262                                   18     40       55       5   263        219                                   19     45       10      45   278        192                                   20     45       25      30   290        195                                   21     45       45      10   259        135                                   ______________________________________                                    

                  TABLE 4-3                                                       ______________________________________                                        Sample CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          Y.sub.2 O.sub.3                                                                    Room Temp                                                                              1000° C.                      ______________________________________                                        1      40      5      10   45   328      300                                  2      40      5      25   30   351      282                                  3      40      5      45   10   343      275                                  4      40     10       5   45   339      351                                  *5     40     10      10   40   370      354                                  *6     40     10      25   25   366      354                                  *7     40     10      40   10   358      362                                  8      40     10      45    5   345      322                                  9      40     25       5   30   333      319                                  *10    40     25      10   25   381      358                                  *11    40     25      20   15   379      380                                  *12    40     25      25   10   368      363                                  13     40     25      30    5   328      332                                  *14    40     40      10   10   367      353                                  15     40     45       5   10   309      303                                  16     40     45      10    5   313      321                                  ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Sample                                                                              CaF.sub.2                                                                              Al.sub.2 O.sub.3                                                                      Si.sub.3 N.sub.4                                                                    Room Temp  1000° C.                       ______________________________________                                         1     5       80      15     29         54                                    2     5       65      30     57         52                                    3     5       50      45     36         23                                    4    10       80      10    245        258                                   *5    10       75      15    310        313                                   *6    10       60      30    316        323                                   *7    10       45      45    304        306                                    8    10       40      50    284        288                                   *9    20       65      15    315        320                                   *10   20       50      30    329        339                                   11    20       30      50    260        272                                   12    30       60      10    289        276                                   *13   30       40      30    337        341                                   *14   30       25      45    318        319                                   15    40       50      10    306        222                                   *16   40       45      15    325        320                                   *17   40       30      30    323        305                                   *18   40       15      45    329        311                                   19    40       10      50    202        219                                   20    45       40      15    269        108                                   21    45       25      30    321        133                                   22    45       10      45    303        135                                   ______________________________________                                    

                  TABLE 6-1                                                       ______________________________________                                        Sample                                                                              CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          Si.sub.3 N.sub.4                                                                    Room Temp                                                                              1000° C.                      ______________________________________                                         1    10      5      70   15    340      316                                   2    10      5      50   35    352      310                                   3    10      5      35   50    315      312                                   4    10     10      70   10    321      304                                  *5    10     10      65   15    366      358                                  *6    10     10      45   35    355      360                                  *7    10     10      20   50    362      361                                   8    10     10      25   55    265      259                                  *9    10     20      20   50    357      366                                  10    10     20      15   55    254      262                                  11    10     25      10   55    239      244                                  12    10     30      50   10    335      314                                  *13   10     30      45   15    368      370                                  *14   10     30      25   35    378      369                                  *15   10     30      10   50    355      361                                  16    10     35       5   50    323      334                                  *17   10     50      20   20    365      362                                  *18   10     50      10   30    359      362                                  19    10     50       5   35    340      351                                  *20   10     65      10   15    358      355                                  21    10     70      10   10    320      313                                  22    10     70       5   15    302      316                                  ______________________________________                                    

                  TABLE 6-2                                                       ______________________________________                                        Sample                                                                              CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          Si.sub.3 N.sub.4                                                                    Room Temp                                                                              1000° C.                      ______________________________________                                         1    30      5      50   15    343      299                                   2    30      5      35   30    352      316                                   3    30      5      20   45    333      304                                   4    30     10      50   10    325      313                                  *5    30     10      45   15    370      370                                  *6    30     10      30   30    367      358                                  *7    30     10      15   45    359      365                                   8    30     10      10   50    258      243                                  *9    30     15      10   45    360      358                                  10    20     20       5   45    303      300                                  11    30     30      30   10    321      304                                  *12   30     30      25   15    376      378                                  *13   30     30      20   20    282      373                                  *14   30     30      10   30    380      377                                  15    30     30       5   35    310      306                                  *16   30     45      10   15    365      368                                  17    30     50      10   10    325      331                                  18    30     50       5   15    330      323                                  ______________________________________                                    

                  TABLE 6-3                                                       ______________________________________                                        Sample                                                                              CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          Si.sub.3 N.sub.4                                                                    Room Temp                                                                              1000° C.                      ______________________________________                                         1    40      5      40   15    344      308                                   2    40      5      25   30    352      327                                   3    40      5      10   45    355      310                                   4    40     10      40   10    343      306                                  *5    40     10      35   15    364      366                                  *6    40     10      20   30    383      373                                  *7    40     10      10   40    360      359                                   8    40     10       5   45    327      339                                   9    40     25      25   10    354      322                                  *10   40     25      20   15    354      351                                  *11   40     25      15   20    374      350                                  *12   40     25      10   25    362      355                                  13    40     25       5   30    341      339                                  *14   40     35      10   15    359      355                                  15    40     40      10   10    323      308                                  16    40     40       5   15    383      315                                  ______________________________________                                    

The joining agent of the above embodiment is applied for the siliconnitride ceramics having a high heat resistance. However, the joiningagent according to the present invention is applicable for a siliconnitride system ceramics including a silicon nitride component such assyaron ceramics.

Further, the joining agent according to the present invention can beprepared by using the compound of alumina and silica such as kaolinite(Al₂ O₃.2SiO₂.2H₂ O) and mullite (3Al₂ O₃.2SiO₂) in place of a mixtureof individual alumina and silica.

In such a way, the joining agent according to the present inventionincludes, as an electric conductive component, CaF₂ and achieves thejoint strength practically usable at high temperature and is verysuitable for joining the ceramic body having a high heat resistance.

Joining Agent For Use in Oxide System Ceramic

In the following embodiments, a joining agent is a mixture of variouspowders in a given mixing ratio and is of a paste form incorporated withorganic binder solved in a solvent such as acetone or toluene. A testpiece for strength test (bending test) is prepared by making jointedsilicon nitride ceramic body obtained by joining two silicon nitridesquare bars in a size of 15 mm×15 mm×20 mm with the joining agent. Aceramic square bar in a size of 3 mm×4 mm×40 mm (JIS size) is obtainedby cutting the jointed ceramic bodies. The used joining agent is in anamount of 50 mg/cm². The strength test is carried out with the testpiece in a JIS format the following condition by using a four pointsbending test: An upper span is 10 mm, and a lower span is 30 mm. Theloading rate is 0.5 mm/min. The testing result is shown by the averagevalue Mpa (mega pascal) obtained with 10 testing pieces subjected to thefour points bending test.

The electric joining method is carried out at the following condition:The pre-heating is carried out up to a temperature of 850° to 900° C.with a mixing gas of propane and oxygen. The flowing electric currentthrough the joining agent is 0.3 to 2 A, the whole of the butted portionto be jointed is heated. In the following embodiment, the table showingexperimental data is described in a collecting manner after descriptionof the invention.

Embodiment 36

The joining agent in a composition of NaF, Al₂ O₃ and SiO₂ in a mixingratio shown in Table 7 is tested with the joint strength at roomtemperature and at 600° C. The joining agent including 5 to 20 weight %of Naf, 20 to 60 weight % of Al₂ O₃ and 30 to 70 weight % of SiO₂ showsthe strength higher than 150 MPa at a temperature range of roomtemperature to 600° C.

The joining agent in a composition of NaF, Al₂ O₃, SiO₂ and MgO in amixing ratio shown in Table 8-1 and 8-2 is tested with the jointstrength at room temperature and at 600° C. The joining agent including5 to 20 weight % of Naf, 20 to 60 weight % of Al₂ O₃, 30 to 70 weight %of SiO₂ and 2.5 to 10 weight % of MgO shows the strength higher than 230MPa at a temperature range of room temperature to 600° C.

Table 9 indicates the test result that the composition having a furtheradditives Y₂ O₃ and TiO₂ is tested with the joint strength at roomtemperature and 600° C.

                  TABLE 7                                                         ______________________________________                                        Sample NaF    Al.sub.2 O.sub.3                                                                        SiO.sub.2                                                                          Room Temp  600° C.                        ______________________________________                                         1     50     20        30   --         --                                     2     30     40        30   165         98                                    3     30     20        50   172         74                                    4     20     60        20   158        131                                   *5     20     50        30   227        157                                   *6     20     30        50   221        163                                   *7     20     20        60   223        151                                    8     20     10        70   196        119                                    9     10     70        20   --         --                                    *10    10     60        30   238        210                                   *11    10     40        50   226        206                                   *12    10     20        70   229        151                                   13     10     10        80   212        108                                   14      5     65        30   153        162                                   *15     5     60        35   233        213                                   *16     5     42        53   235        202                                   *17     5     25        70   216        162                                   18      5     20        75   201        113                                   19      3     60        37   --         --                                    20      3     47        50    38         42                                   21      3     27        70   --         --                                    ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                                                                 Room                                 Sample                                                                              NaF    Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          MgO  Y.sub.2 O.sub.3                                                                    TiO.sub.2                                                                          Temp  600° C.                 ______________________________________                                        1     10     45      40   5    2.5  2.5  292   242                            2     10     35      45   2.5  2.5  5    288   246                            3     10     30      50   5    2.5  2.5  285   236                            4     10     36      46.5 --   7.5  --   284   243                            5     10     38.3    49   --   --   2.5  279   238                            ______________________________________                                    

The above embodiment uses, as an oxide ceramic body, aluminum oxide butthe joining agent according to the present invention is applicable foran oxide ceramic such as mullite and ZrO₂.

Further, the joining agent according to the present invention can beprepared by using the compound of alumina and silica such as kaolinite(Al₂ O₃.2SiO₂. 2H₂ O) and mullite (3Al₂ O₃. 2SiO₂) in place of a mixtureof individual alumina and silica.

In order to give the joining agent according to the present inventionanother effect or improved effect, it is possible to add the variousadditives into the joining agent according to the present invention. Forexample, the joining agent according to the present invention can havenitride such as Si₃ N₄ or AlN and carbide such as SiC or TiNincorporated therein in order to include N or C in the glass of thejoint layer. Various properties of the joint layer are improved by theformation of oxynitride glass or oxycarbide glass.

The present invention can provide a joining agent suitable for joiningthe oxide ceramic by using, as a electric conducive component, NaF. Thejoining agent according to the present invention does not impair theceramic body and ensures the excellent sealing property and the jointstrength at room temperate to a high temperature, which is practicallyusable.

Joining Agent using a fluoride of a third element

Embodiment 37

A joining agent used is composed of a mixture of 60 weight % of YF₃, 20weight % of Al₂ O₃ and 20 weight % of SiO₂.

A test piece for strength test is prepared by the jointed siliconnitride ceramic body obtained by joining two silicon nitride ceramicsquare bars in a size of 15 mm×15 mm×20 mm with the joining agent in anamount of 50 mg/cm². The silicon nitride ceramic bodies with the joiningagent is heated by an electric current of 0.6 to 1.0 A for 5 to 10 minunder moving the electrode at a rate of 5 cm/min.

A ceramic square bar in a size of 3 mm×4 mm×40 mm is obtained by cuttingthe jointed ceramic bodies. The strength test is carried out with thetest piece at the following condition by using a three points bendingtest: A span is 30 mm, and the loading rate is 0.5 mm/min. The testingresult is shown by the average value Mpa (mega pascal) obtained withthree testing pieces. The resultant strength is 420 Mpa at roomtemperature and is kept nearly to 420 MPa at 1050° C. as shown in Table10.

                  TABLE 10                                                        ______________________________________                                                   Unit: MPa                                                                      Room Tem-                                                         Main Ingredient                                                                           perature     1000° C.                                                                        1050° C.                             ______________________________________                                        (Conventional)                                                                            400          350       35                                         CaF--Al.sub.2 O.sub.3 --SiO.sub.2                                             (Invention) 421          419      413                                         Y.sub.2 O.sub.3 --Al.sub.2 O.sub.3 --SiO.sub.2                                ______________________________________                                    

Embodiment 38

A joining agent used here is composed of a mixture of 50 weight % ofScF₃, 25 weight % of Al₂ O₃ and 25 weight % of SiO₂. Two ceramic bodiesare jointed by using the above joining agent and is tested with thejointed strength in a similar way to that of the embodiment 37. As shownin Table 11, the strength is 416 MPa at a temperature from roomtemperature to 1050° C.

                  TABLE 10                                                        ______________________________________                                                   Unit: MPa                                                                      Room Tem-                                                         Main Ingredient                                                                           perature     1000° C.                                                                        1050° C.                             ______________________________________                                        (Conventional)                                                                            400          350       35                                         CaF--Al.sub.2 O.sub.3 --SiO.sub.2                                             (Invention) 421          419      413                                         ScF.sub.3 --Al.sub.2 O.sub.3 --SiO.sub.2                                      ______________________________________                                    

The joining agent according to the present invention is applicable foran oxide ceramic such as Al₂ O₃ and ZrO₂ and non-oxide ceramic such assyaron in addition to Si₃ N₄.

Further, the joining agent according to the present invention can beprepared by using the compound of alumina and silica such as kaolinite(Al₂ O₃. 2SiO₂. 2H₂ O) and mullite (3Al₂ O₃. 2SiO₂) in place of amixture of individual alumina and silica.

In order to give the joining agent according to the present inventionanother effect or improved effect, it is possible to add the variousadditives besides the third group element fluoride and Al₂ O₃, SiO₂ intothe joining agent according to the present invention. For example, thejoining agent according to the present invention can have nitride suchas Si₃ N₄ or AlN and carbide such as SiC or TiN incorporated therein inorder to include N or C in the glass of the joint layer. Variousproperties of the joint layer are improved by the formation ofoxynitride glass or oxycarbide glass.

The joining agent according to the present invention comprises, as amain ingredient, YF₃ or the combination of YF₃ and at least one elementselected from the group consisting of Al₂ O₃ and SiO₂. The jointstrength, especially at high temperature, and the corrosion resistanceto alkali or acid are extremely improved by using the joining agentaccording to the present invention.

What is claimed is:
 1. A method for electrically joining two bodies tobe jointed, one of said bodies being a ceramic body, comprising thesteps of: inserting a joining agent, or a combination of a joining agentand an inserting member for heating based on an electrically conductiveceramic material, between butted planes to be jointed of said twobodies, causing said joining agent to melt and react by a Joule heatingand joining said two bodies to be jointed, further comprising,contactingthree or more electrodes positioned a given interval apart, forsupplying electric current and generating Joule heating, at the surfaceof a current-flowing member selected from the group consisting of saidbodies to be jointed, said joining agent, and said inserting member forheating, and supplying current to said current-flowing member between atleast two electrodes selected sequentially from said three or moreelectrodes in accordance with a given electrode switching pattern tomove a current flowing area along said butted portion to be jointedwherein the current supplying step is carried out with an electrodeswitching pattern which is selected from a plurality of electrodeswitching patterns in accordance with a variation in the condition atsaid butted portion to be jointed.
 2. A method for electrically joiningtwo bodies to be jointed, one of said bodies being a ceramic body,according to claim 1, wherein the current supplying step is carried out,at an initial current-flowing stage, with an electrode switching patternto cause the current supplied between the electrodes to have a shortcurrent-flowing distance, and then with an electrode switching patternto cause the current supplied between the electrodes to have a longercurrent-flowing distance.
 3. A method for electrically joining twobodies to be jointed, one of said bodies being a ceramic body, accordingto any one of claims 1 or 2, wherein the current supplying step iscarried out with an electrode switching pattern to overlap partially aprevious current flowing area with a next current flowing area.
 4. Amethod for electrically joining two bodies to be jointed, one of saidbodies being a ceramic body, according to any one of claims 1 or 2,wherein said electrode switching pattern is combined with at least onecurrent supplying condition selected from the group consisting of (a) acurrent supplying condition to heat uniformly said butted portion to bejointed by changing at least one of the electric current, electricpower, and an energizing holding time in accordance with the conditionof the butted portion to be jointed varying with the current supplyingposition and (b) a current supplying condition to release a thermalshock of the bodies to be jointed or to promote the reaction of saidjoining agent by changing at least one of the electric current, electricpower, and an energizing holding time with a time passage in accordancewith a predetermined temperature control pattern.
 5. A method forelectrically joining two bodies to be jointed, one of said bodies beinga ceramic body, according to any one of claims 1 or 2, wherein saidthree or more electrodes are classified into a plurality of groups ofelectrodes, each of which is controlled in the current supplying step inaccordance with a given electrode switching pattern and a given currentsupplying condition.
 6. A method for electrically joining two bodies tobe jointed, one of said bodies being a ceramic body, according to claim5, wherein each of said plurality of groups of electrodes is controlledin the current supplying step with an independent current supplyingcontrol apparatus.